James M. Ntambi
Sep 1, 1999; 40:1549-1558
Reviews

M el-Saadani
Apr 1, 1989; 30:627-630
Articles

Jason M. Ridlon
Feb 1, 2006; 47:241-259
Reviews

The UK's new Online Safety Bill 10 February 2021 — 3:00PM TO 3:45PM Anonymous (not verified) 26 January 2021 Online

Discussing the new proposals which include the establishment of a new ‘duty of care’ on companies to ensure they have robust systems in place to keep their users safe.

Governments, regulators and tech companies are currently grappling with the challenge of how to promote an open and vibrant internet at the same time as tackling harmful activity online, including the spread of hateful content, terrorist propaganda, and the conduct of cyberbullying, child sexual exploitation and abuse.

The UK government’s Online Harms proposals include the establishment of a new ‘duty of care’ on companies to ensure they have robust systems in place to keep their users safe. Compliance with this new duty will be overseen by an independent regulator.

On 15 December 2020, DCMS and the Home Office published the full UK government response, setting out the intended policy positions for the regulatory framework, and confirming Ofcom as the regulator.

With the legislation likely to be introduced early this year, the panel will discuss questions including:

• How to strike the balance between freedom of expression and protecting adults from harmful material?

• How to ensure the legislation’s approach to harm is sufficiently future-proofed so new trends and harms are covered as they emerge?

• What additional responsibilities will tech companies have under the new regulation?

• Will the regulator have sufficient powers to tackle the wide range of harms in question?

This event is invite-only for participants, but you can watch the livestream of the discussion on this page at 15.00 GMT on Wednesday 10 February.

Strengthening Transatlantic Digital Cooperation

This project explores opportunities for increased cooperation via the transatlantic ‘tech triangle’ of the European Union, United Kingdom and United States.

This project serves as a cross-house initiative (involving the US and Americas Programme, the Europe Programme, the International Law Programme, the Digital Society Initiative and the International Security Programme).

Its long-term goal is to support the emergence of a global vision for technology governance: a vision drawing on democratic values and human rights principles. The project aims to extend the application of these principles to the digital space.

The first phase centres around a knowledge-exchange series, with findings and recommendations disseminated around targeted multilateral events such as G7, the United Nations General Assembly and the 2021 Internet Governance Forum.

Building on this exchange, the second phase will shift its focus to other democratic states and broaden digital cooperation dialogues from like-minded countries in the OECD, in addition to non-Western democracies and under-represented stakeholders from developing countries.

Counter-terrorism measures and sanctions: How to avoid negative consequences for humanitarian action? 9 September 2021 — 2:00PM TO 3:30PM Anonymous (not verified) 21 July 2021 Online

Exploring current endeavours to address the tensions between counter-terrorism measures, sanctions and humanitarian action.

Counter-terrorism measures  address broad forms of support to terrorist acts. Their expansion, internationally and domestically, has given rise to new points of friction with international humanitarian law. Unless the measures include adequate safeguards, they  can impede humanitarian action. Country-specific sanctions imposed for other objectives, such as ending conflicts or protecting civilians, raise similar challenges for humanitarian action. 

These problems are not new, but solutions at international and national level remain elusive. 

At this panel event, which marks the launch of a new Chatham House research paper, panellists explore current endeavours to address the tensions between counter-terrorism measures, sanctions and humanitarian action.

• What are the current dynamics and developments at Security Council level?  
• What are the opportunities now that the UK is developing its independent sanctions strategy? 
• What challenges do counter-terrorism requirements in funding agreements for humanitarian action  pose? 
• What is necessary to make progress?

Protecting universal human rights: Imagine a better world Explainer Video NCapeling 19 November 2021

Short animation examining why protecting and defending human rights ensures an equitable response to humanitarian crises and addresses economic inequality.

Human rights are not policies that can be overturned, they are not granted by governments. They belong to everyone as human beings.

For the most part, states are meeting their commitments to defend and protect universal human rights. But increasingly some governments are beginning to shy away from their obligations, and some are even actively seeking to subvert human rights.

And the regional and international bodies created and charged with defending these rights are being challenged by the rise of new powers and political movements.

Chatham House is built on big ideas. Help us imagine a better world.

Our researchers develop positive solutions to global challenges, working with governments, charities, businesses and society to build a better future.

SNF CoLab is our project supported by the Stavros Niarchos Foundation (SNF) to share our ideas in experimental, collaborative ways – and to learn about designing a better future.

Transatlantic Tech Talks: Cooperation or sovereignty? Audio bhorton.drupal 15 December 2021

A new mini-series from Undercurrents explores international cooperation on regulating the tech sector.

Transatlantic Tech Talks is a three part mini-series on the Undercurrents podcast feed, produced with the support of Microsoft, which explores the state of international cooperation on digital governance between the United States, the UK and Europe.

As technological innovation accelerates, and new digital tools and business models arise, governments are working to develop a framework of regulations to safeguard the rights and interests of their citizens. Not all stakeholders agree, however, on the best way to achieve this. While some advocate a ‘digital cooperation’ approach based on transparency and data-sharing, others are more concerned with maintaining ‘digital sovereignty’.

In the first episode of this series, Ben is joined by Casper Klynge, Harriet Moynihan and Marianne Schneider-Petsinger, who set out the broad context for these debates. They assess where the major government, private sector and civil society actors stand on the question of digital governance, and how they are approaching the international negotiations.

Sanctions must not prevent humanitarian work in Ukraine Expert comment NCapeling 30 May 2022

Restrictions on supply of certain items and financial sanctions can impede vital relief unless adequate safeguards are put in place such as exceptions or general licences.

Sanctions play a major role in the response to Russia’s invasion of Ukraine. The United Nations (UN) has not imposed sanctions, but an important number of states have done so. They have imposed a wide array of restrictions and the number of targeted – or ‘designated’ – persons is unprecedented.

The public has been captivated by the freezing of oligarchs’ assets. There is ongoing discussion about seizing them to provide compensation for war damage. Debate continues about how far to ban oil and gas imports.

One aspect of the sanctions has received far less attention, even though it can exacerbate the effect of the conflict on civilians. Some of the trade restrictions and financial sanctions pose immediate and concrete challenges to the capacity of humanitarian organizations to work in Ukraine and in neighbouring states.

Trade sanctions imposed by the European Union (EU) and UK prohibit the export or supply of certain goods and technology in the transport, telecommunications, energy, and oil or mineral exploration sectors to non-government-controlled areas of the Donetsk or Luhansk oblasts, or for use there.

Restricted items include technical equipment which is necessary for humanitarian operations, such as water pumps and refrigerating equipment, but also far more mundane items such as vehicles for transport of persons and goods, and office equipment that are necessary for humanitarian organizations trying to work in the region.

Designations can reduce options for support

Financial sanctions also raise problems. Some are immediately apparent. Significantly for humanitarian operations, the two de facto republics of Donetsk and Luhansk are designated by the EU, the UK, and the US. Consequently, it is prohibited to make funds or assets available to them directly or indirectly.

This prohibition covers the payment of any taxes, licences, and other fees to these authorities, as well as the provision of assets to ministries under their control in the course of humanitarian operations, such as ministries of health and education.

Designations of other entities may also be relevant, such as Russian ‘state enterprises’ which operate in these areas and are the sole providers of commodities necessary for humanitarian response, such as heating fuel.

These are the designations which most obviously impact humanitarian response. However, more than 1,000 persons and entities have been designated and humanitarian organizations must avoid purchasing goods and services from them.

Risk-averse commercial partners

Commercial actors – such as banks, insurers, freight companies and commodity providers – whose services are required by humanitarian organizations must also comply with the sanctions. Experience shows that the due diligence measures adopted by humanitarian organizations do not always allay concerns of risk-averse sectors such as banks.

Fears of violating the sanctions, coupled with the fact humanitarian organizations are rarely profitable clients, have led them to severely restrict the services they provide.

This is not the first occasion the problem has arisen. What is different in relation to Ukraine is the number of designated persons and the ‘sanctions packages’ adopted in quick succession. As compliance officers struggle to keep abreast, their institutions become even more risk-averse.

For UK banks, the situation is exacerbated by the adoption of the Economic Crime (Transparency and Enforcement) Act 2022. This amends existing rules by removing the requirement for the UK Treasury to prove knowledge or reasonable cause to suspect that a transaction violated sanctions, imposing strict liability for sanctions violations.

Time for the UK to follow others

The EU, the US, Switzerland, and other states which have imposed sanctions have sought to mitigate their adverse effects by including safeguards for humanitarian action. Although the UK has largely replicated the measures adopted by the EU in terms of restrictions and designations, it lags behind in including such safeguards.

The UK trade restrictions and financial sanctions do not include exceptions for humanitarian action. While several general licences have been issued, none relate to humanitarian operations.

Instead, the UK measures foresee only the possibility of applying for specific licences – from the Treasury in the case of financial sanctions and the Department of International Trade for trade restrictions. But obtaining specific licences is a time-consuming process which is simply not appropriate for emergency response.

If the UK is to show it is serious about responding to the immense needs caused by the invasion it must introduce appropriate safeguards in its sanctions – either in the form of exceptions or general licences.

What matters is they cover all key humanitarian organizations responding to the Ukraine crisis that are subject to UK sanctions – either because they are UK persons or because their funding agreements with the UK government require them to comply with UK measures.

These include UN agencies, funds and programmes, components of the International Red Cross and Red Crescent Movement, and non-governmental organizations (NGOs) responding to the crisis in Ukraine and neighbouring states. The provision must also clearly extend to commercial entities which provide necessary services for humanitarian operations.

Given the UK recently adopted an exception along similar lines in relation to the Afghanistan sanctions, there is a valuable precedent for Ukraine.

Humanitarian exceptions: A turning point in UN sanctions Expert comment LJefferson 20 December 2022

The UN Security Council has adopted a cross-cutting exception for humanitarian action in UN sanctions. What does it cover? What must happen next?

The UN Security Council has removed an obstacle to humanitarian work. On 9 December 2022, it adopted a resolution establishing a cross-cutting exception to existing – and future – UN financial sanctions for funds or assets necessary for humanitarian assistance and activities to meet basic human needs. In a coup for multilateralism, the council has been able to act, even when the Russian invasion of Ukraine has caused paralysis in other areas.

Resolution 2664 – introduced by Ireland and the US, co-sponsored by 53 states, and adopted by 14 votes in favour, with India abstaining – is the culmination of a decade of engagement between humanitarian organizations and states to find ways of avoiding the adverse impact of sanctions on the most vulnerable: people relying on humanitarian action for survival.

A reminder of the problem

Whilst sanctions are not intended to have adverse humanitarian consequences for civilian populations, aid agencies have argued for years that they do just this. UN financial sanctions prohibit making funds or other assets available directly or indirectly to designated persons or entities. Without adequate safeguards, incidental payments made during humanitarian operations, or relief consignments that are diverted and end up in the hands of such persons or entities can violate this prohibition.

Exceptions in Afghanistan and Haiti sanctions pave the way

Humanitarian actors have been decrying and documenting the impact of sanctions on their operations for years. Ensuring that sanctions did not hinder the COVID-19 response was a turning point in states’ willingness to address the issue.

Movement at Security Council level was gradual, starting off with demands in the renewals of certain country-specific sanctions that measures taken by member states to give effect to them comply with international law. The return to power of the Taliban called for a more radical approach.

In December 2021, the Council adopted a broad exception to the Afghanistan financial sanctions, covering the provision, payment and processing of funds and assets necessary for humanitarian action and for activities to meet basic human needs. A similar exception was adopted – almost unnoticed – in October 2022 in the newly-established Haiti sanctions.

These developments, coupled with the determination of elected Council member Ireland to find solutions, paved the way for the adoption of SCR 2664.

The scope of the humanitarian exception

SCR 2664 introduces a clear and broad exception that addresses the key challenges financial sanctions pose to humanitarian action. The exception expressly refers to the different ways in which funds or assets are allowed to reach designated persons or entities: by the provision of goods or payment of funds by humanitarian actors themselves; by the processing of funds by financial institutions; and by the provision of goods and services by other commercial actors whose services are necessary for humanitarian action such as insurers and freight companies.

The exception is broad in terms of the excluded activities: the provision of funds and assets necessary for humanitarian assistance and activities to meet basic human needs. The UN Somalia sanctions – the first, and for a decade the only, regime to include an express exception – exclude funds necessary for ‘humanitarian assistance’.

SCR 2615 on Afghanistan added the expression ‘activities to meet basic human needs’.  These go beyond humanitarian assistance, and have been interpreted as including activities necessary to sustain essential social services such as health and education, preserve essential community systems, and promote livelihoods and social cohesion.  These are essentially development programmes.  ‘Activities that support basic needs’ should be understood in a similar manner in SCR 2664.

SCR 2664 is not, however, a ‘blanket’ exception.  It only applies to financial sanctions.  These are not the only type of restriction in UN sanctions that can hinder humanitarian action. For example, organizations that send commodities into the Democratic People’s Republic of Korea must still go through the notoriously slow procedure of authorization by the sanctions committee.  Similarly, authorizations are still required for import of demining materials that fall within the scope of arms embargoes.

Opportunities for further engagement and additional safeguards

Recognizing that additional challenges remain, SCR 2664 requests the UN Secretary-General to draft a report on unintended adverse humanitarian consequences of all types of restrictions in UN sanctions. He is asked to include recommendations for minimizing and such unintended consequences, including by the adoption of additional cross-cutting exceptions.

Humanitarian organizations have played a pivotal role in advancing the agenda. SCR 2664 is the result of their relentless engagement with the Security Council. It is not the end of the road. Other restrictions raise problems, and the Council has left the door open to finding ways of addressing them.

Humanitarian actors should seize this opportunity to provide information, identifying the problematic types of restrictions and their consequences on their operations as specifically as possible.

What happens next?

It is UN member states that implement UN sanctions. For SCR 2664 to be truly effective, it is imperative that states give effect to it in domestic law and practice. In doing so, they must not narrow the scope of the exception.

Recent experience in Afghanistan has shown that even in situations when significant safeguards exist, key actors may be unaware of them or unclear as to their precise scope. Financial institutions in particular are fast to de-risk when sanctions are imposed, and remain wary of conducting transactions that they perceive as high-risk even though exceptions permit this.

OFAC – the Office of Foreign Assets Control in the US Treasury – has issued extensive guidance on the Afghanistan sanctions in the form of frequently asked questions.  These have played an extremely important role in ensuring full advantage is taken of the exceptions.

States should follow this example, and adopt guidance to raise awareness of the exception in SCR 2664 and to clarify its scope.

A valuable precedent for autonomous sanctions

SCR 2664 only applies to sanctions adopted by the UN Security Council. It does not extend to autonomous sanctions adopted by states or relevant international organizations such as the EU.

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Centrioles are key eukaryotic organelles that are responsible for the formation of cilia and flagella, and for organizing the microtubule network and the mitotic spindle in animals. Centriole assembly requires oligomerization of the essential protein spindle assembly abnormal 6 (SAS-6), which forms a structural scaffold templating the organization of further organelle components. A dimerization interaction between SAS-6 N-terminal “head” domains was previously shown to be essential for protein oligomerization in vitro and for function in centriole assembly. Here, we developed a pharmacophore model allowing us to assemble a library of low-molecular-weight ligands predicted to bind the SAS-6 head domain and inhibit protein oligomerization. We demonstrate using NMR spectroscopy that a ligand from this family binds at the head domain dimerization site of algae, nematode, and human SAS-6 variants, but also that another ligand specifically recognizes human SAS-6. Atomistic molecular dynamics simulations starting from SAS-6 head domain crystallographic structures, including that of the human head domain which we now resolve, suggest that ligand specificity derives from favorable Van der Waals interactions with a hydrophobic cavity at the dimerization site.

Driven to Extraction: Can Sand Mining be Sustainable? 5 June 2019 — 1:30PM TO 3:00PM Anonymous (not verified) 29 April 2019 Chatham House | 10 St James's Square | London | SW1Y 4LE

Sand: Monitoring and management for a sustainable future 2 March 2021 — 1:00PM TO 2:00PM Anonymous (not verified) 18 February 2021 Online

In partnership with the Global Sand Observatory Initiative, this event outlines the sand challenge, what actions are currently underway to address it, and what else needs to be done.

Please complete your registration on Zoom:

After water, sand is the raw material that the world consumes in the greatest quantity. It is no exaggeration to say that fine sand and coarser materials – the medium-to-coarse-grained pebbles, gravel and rock fragments used in construction – are the building blocks of the modern world.

When bound with cement, sand becomes concrete; when mixed with bitumen, it becomes asphalt; and when heated, it becomes glass. Without sand, we would have no highways, high-rises or high-speed trains. Yet sand – which is used here as shorthand for sand, gravel and crushed rock together – is a resource that is both abundant and finite.

In global terms, it is abundant, especially when compared with many other raw materials, albeit often not available close to where it is needed. It is finite in that the rate at which we are using it far exceeds the natural rate at which it is being replenished by the weathering of rocks by wind and water.

Industrialization, population growth and urbanization have fuelled explosive growth in the demand for sand. Precise data on sand extraction are hard to come by and the lack of data compounds the challenge of managing the resource sustainably.

However, the UN estimates that overall extraction could be in the region of 40 billion tonnes per year, driven primarily by construction sector demand. That equates to 18 kilograms of sand each day for every person on the planet and signals how strategically important these resources are for future sustainable development. Post-COVID-19 recovery investment in infrastructure, digital technologies, tourism and other economic activities are dependent on sand resources.

Current efforts to improve the management of sand resources at local, national and global levels are uneven. This is partly due to unique geological features and geography, but also differences in local manifestations of the ‘sand challenge’, national and regional demand for sand resources, as well as capacities to enforce or implement best practice assessment procedures, extractive practices, environmental management and restoration requirements.

We must put stronger conditions in place for a rapid, just and scaled transition to sustainable sand management. But where to focus our efforts for the greatest positive impact?

Anne-Miek Bibbe posted a photo:

JOEPIE: I'm almost there! I wish Uncle Jeroen was here, I'm a little, really just a little bit afraid of the dark.
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JOEPIE: Ik ben bijna bij Peter! Ik wou dat oom Jeroen hier was, ik ben een beetje, echt maar een héél klein beetje bang in het donker.

Marko Voutilainen, Lauri Viitasaari and Pauliina Ilmonen
Theor. Probability and Math. Statist. 111 (), 181-197.
Abstract, references and article information

Bo Shan Deval, Xabier García-Martínez and Tim Van der Linden
Proc. Amer. Math. Soc. 152 (), 5039-5053.
Abstract, references and article information

Ana Caraiani, Royal Society University Research Fellow and professor of pure mathematics, Imperial College London, has been awarded the 2025 Ruth Lyttle Satter Prize in Mathematics by the American Mathematical Society (AMS). She has been honored for contributions to arithmetic geometry and number theory: in particular, the Langlands program.

From the citation

Ana Caraiani’s work is characterized by a combination of novel ideas and a fearlessness in the face of technical obstacles that would daunt almost any other researcher. This has enabled her to prove several fundamental theorems in the Langlands program.

In the joint paper with Scholze, titled “On the generic part of the cohomology of non-compact unitary Shimura varieties” (Annals of Math., 2024), Caraiani proved very general results about the torsion cohomology classes in non-compact Shimura varieties, strengthening the early results in their 2017 paper in the compact case. The proof is a tour de force, combining perfectoid spaces, a mastery of the trace formula, and a new theory of perverse sheaves in p-adic geometry. These results are of intrinsic interest (for example, they give the first indications of a characteristic p version of Arthur’s conjectures), but they also have many applications throughout the Langlands program. One spectacular application of these results is in her joint paper, “Potential automorphy over CM fields” (with Allen, Calegari, Gee, Helm, Le Hung, Newton, Scholze, Taylor, and Thorne, Annals of Math., 2023), which among other results proves the Ramanujan conjecture for Bianchi modular forms, a problem that had been thought of as being completely out of reach.

The Ramanujan conjecture is of analytic nature, asserting a bound on the eigenvalue of a certain differential operator, but the only way in which cases of it have been proved is via algebraic geometry. In particular, the original Ramanujan conjecture for modular forms was proved by Deligne in the 1970s, as a consequence of his proof of the Weil conjectures. However, in the case of Bianchi modular forms there is no direct relationship with algebraic geometry, and it seems to be impossible to make any direct deductions from the Weil conjectures. Langlands (also in the 1970s) suggested a strategy for proving the Ramanujan conjecture as a consequence of his functoriality conjecture. Caraiani and her coauthors’ proof of the Ramanujan conjecture for Bianchi modular forms proceeds via a variant of Langlands’ strategy, and in particular does not use the Weil conjectures.

Most recently with James Newton, in the paper “On the modularity of elliptic curves over imaginary quadratic fields” (arXiv: 2301.10509), Caraiani has improved upon these results and applied them to the modularity of elliptic curves over imaginary quadratic fields. They come close to completely solving it, with only a small number of exceptions (which constitute 0% of cases).

Response of Ana Caraiani

First, I would like to thank Joan Birman and the AMS for establishing an award that recognizes research contributions by women mathematicians. This is particularly meaningful to me because I looked to many of the previous recipients of the Satter Prize for inspiration at challenging moments in my career. It is a great honour to be selected as a recipient!

I am indebted to my many collaborators, mentors and colleagues who have generously shared their mathematical ideas with me over the years and supported me in different but crucial ways. Special thanks go to Peter Scholze for the wonderful opportunity to collaborate with him on understanding a part of the geometry and cohomology of Shimura varieties, to Richard Taylor for initiating the "ten author" collaboration, which was much more successful than we had originally expected, and to James Newton for our joyful exploration of elliptic curves over imaginary quadratic fields. I also particularly want to acknowledge Jessica Fintzen and Toby Gee for their longstanding friendship and moral support.

Finally, I want to thank my family, especially my husband, Steven, my mother, Zoe, and my daughter, Nadia.

Biographical sketch of Ana Caraiani

Ana Caraiani was born in Bucharest, Romania, in 1984. She received a bachelor's degree in mathematics from Princeton University in 2007 and completed her PhD at Harvard University in 2012. After temporary positions at the University of Chicago, Princeton and the Institute for Advanced Study (IAS), and the University of Bonn, she moved to Imperial College London in 2017, where she is currently a Royal Society University Research Fellow and Professor of Pure Mathematics. She is a Fellow of the AMS, a recipient of an EMS Prize and a New Horizons Prize in Mathematics and was an invited speaker at the 2022 ICM. 

About the prize

Awarded every two years, the Ruth Lyttle Satter Prize in Mathematics recognizes an outstanding contribution to mathematics research by a woman in the previous six years. The prize was established by Joan Birman in honor of her sister, Ruth. The 2025 prize will be recognized during the 2025 Joint Mathematics Meetings in January in Seattle.

Read more and see the list of past recipients.

Contact: AMS Communications

* * * * *

The American Mathematical Society is dedicated to advancing research and connecting the diverse global mathematical community through our publications, meetings and conferences, MathSciNet, professional services, advocacy, and awareness programs.

A police sergeant who was shot and injured at his home in Portmore, St Catherine, on Thursday night succumbed to his injuries on Monday morning.

When using the distinct count function in SAS Visual Analytics reports, you might find that a negative value is displayed instead of the actual distinct count: imgalt="distinct_count" src="{fusion_66562_1_disti

If you connect to a FTP/TLS server that is configured to use implicit FTP/TLS, FILENAME FTP/TLS might fail with the following error:

Animals can sense the presence of microbes in their tissues and mobilize their own defenses by recognizing and responding to conserved microbial structures (often called microbe-associated molecular patterns (MAMPs)). Successful host defenses may kill the invaders, yet the host animal may fail to restore homeostasis if the stimulatory microbial structures are not silenced. Although mice have many mechanisms for limiting their responses to lipopolysaccharide (LPS), a major Gram-negative bacterial MAMP, a highly conserved host lipase is required to extinguish LPS sensing in tissues and restore homeostasis. We review recent progress in understanding how this enzyme, acyloxyacyl hydrolase (AOAH), transforms LPS from stimulus to inhibitor, reduces tissue injury and death from infection, prevents prolonged post-infection immunosuppression, and keeps stimulatory LPS from entering the bloodstream. We also discuss how AOAH may increase sensitivity to pulmonary allergens. Better appreciation of how host enzymes modify LPS and other MAMPs may help prevent tissue injury and hasten recovery from infection.

Myelination plays an important role in cognitive development and in demyelinating diseases like multiple sclerosis (MS), where failure of remyelination promotes permanent neuro-axonal damage. Modification of cell surface receptors with branched N-glycans coordinates cell growth and differentiation by controlling glycoprotein clustering, signaling, and endocytosis. GlcNAc is a rate-limiting metabolite for N-glycan branching. Here we report that GlcNAc and N-glycan branching trigger oligodendrogenesis from precursor cells by inhibiting platelet-derived growth factor receptor-α cell endocytosis. Supplying oral GlcNAc to lactating mice drives primary myelination in newborn pups via secretion in breast milk, whereas genetically blocking N-glycan branching markedly inhibits primary myelination. In adult mice with toxin (cuprizone)-induced demyelination, oral GlcNAc prevents neuro-axonal damage by driving myelin repair. In MS patients, endogenous serum GlcNAc levels inversely correlated with imaging measures of demyelination and microstructural damage. Our data identify N-glycan branching and GlcNAc as critical regulators of primary myelination and myelin repair and suggest that oral GlcNAc may be neuroprotective in demyelinating diseases like MS.

VAR2CSA is the placental-malaria–specific member of the antigenically variant Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family. It is expressed on the surface of Plasmodium falciparum-infected host red blood cells and binds to specific chondroitin-4-sulfate chains of the placental proteoglycan receptor. The functional ∼310 kDa ectodomain of VAR2CSA is a multidomain protein that requires a minimum 12-mer chondroitin-4-sulfate molecule for specific, high affinity receptor binding. However, it is not known how the individual domains are organized and interact to create the receptor-binding surface, limiting efforts to exploit its potential as an effective vaccine or drug target. Using small angle X-ray scattering and single particle reconstruction from negative-stained electron micrographs of the ectodomain and multidomain constructs, we have determined the structural architecture of VAR2CSA. The relative locations of the domains creates two distinct pores that can each accommodate the 12-mer of chondroitin-4-sulfate, suggesting a model for receptor binding. This model has important implications for understanding cytoadherence of infected red blood cells and potentially provides a starting point for developing novel strategies to prevent and/or treat placental malaria.

The bacterial enhancer-binding protein (bEBP) FlrC, controls motility and colonization of Vibrio cholerae by regulating the transcription of class-III flagellar genes in σ54-dependent manner. However, the mechanism by which FlrC regulates transcription is not fully elucidated. Although, most bEBPs require nucleotides to stimulate the oligomerization necessary for function, our previous study showed that the central domain of FlrC (FlrCC) forms heptamer in a nucleotide-independent manner. Furthermore, heptameric FlrCC binds ATP in “cis-mediated” style without any contribution from sensor I motif 285REDXXYR291 of the trans protomer. This atypical ATP binding raises the question of whether heptamerization of FlrC is solely required for transcription regulation, or if it is also critical for ATPase activity. ATPase assays and size exclusion chromatography of the trans-variants FlrCC-Y290A and FlrCC-R291A showed destabilization of heptameric assembly with concomitant abrogation of ATPase activity. Crystal structures showed that in the cis-variant FlrCC-R349A drastic shift of Walker A encroached ATP-binding site, whereas the site remained occupied by ADP in FlrCC-Y290A. We postulated that FlrCC heptamerizes through concentration-dependent cooperativity for maximal ATPase activity and upon heptamerization, packing of trans-acting Tyr290 against cis-acting Arg349 compels Arg349 to maintain proper conformation of Walker A. Finally, a Trp quenching study revealed binding of cyclic-di-GMP with FlrCC. Excess cyclic-di-GMP repressed ATPase activity of FlrCC through destabilization of heptameric assembly, especially at low concentration of protein. Systematic phylogenetic analysis allowed us to propose similar regulatory mechanisms for FlrCs of several Vibrio species and a set of monotrichous Gram-negative bacteria.

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