Myostatin (or growth/differentiation factor 8 (GDF8)) is a member of the transforming growth factor β superfamily of growth factors and negatively regulates skeletal muscle growth. Its dysregulation is implicated in muscle wasting diseases. SRK-015 is a clinical-stage mAb that prevents extracellular proteolytic activation of pro- and latent myostatin. Here we used integrated structural and biochemical approaches to elucidate the molecular mechanism of antibody-mediated neutralization of pro-myostatin activation. The crystal structure of pro-myostatin in complex with 29H4-16 Fab, a high-affinity variant of SRK-015, at 2.79 Å resolution revealed that the antibody binds to a conformational epitope in the arm region of the prodomain distant from the proteolytic cleavage sites. This epitope is highly sequence-divergent, having only limited similarity to other closely related members of the transforming growth factor β superfamily. Hydrogen/deuterium exchange MS experiments indicated that antibody binding induces conformational changes in pro- and latent myostatin that span the arm region, the loops contiguous to the protease cleavage sites, and the latency-associated structural elements. Moreover, negative-stain EM with full-length antibodies disclosed a stable, ring-like antigen–antibody structure in which the two Fab arms of a single antibody occupy the two arm regions of the prodomain in the pro- and latent myostatin homodimers, suggesting a 1:1 (antibody:myostatin homodimer) binding stoichiometry. These results suggest that SRK-015 binding stabilizes the latent conformation and limits the accessibility of protease cleavage sites within the prodomain. These findings shed light on approaches that specifically block the extracellular activation of growth factors by targeting their precursor forms.

Cytochrome c oxidase (CcO) reduces O2 to water, coupled with a proton-pumping process. The structure of the O2-reduction site of CcO contains two reducing equivalents, Fea32+ and CuB1+, and suggests that a peroxide-bound state (Fea33+–O−–O−–CuB2+) rather than an O2-bound state (Fea32+–O2) is the initial catalytic intermediate. Unexpectedly, however, resonance Raman spectroscopy results have shown that the initial intermediate is Fea32+–O2, whereas Fea33+–O−–O−–CuB2+ is undetectable. Based on X-ray structures of static noncatalytic CcO forms and mutation analyses for bovine CcO, a proton-pumping mechanism has been proposed. It involves a proton-conducting pathway (the H-pathway) comprising a tandem hydrogen-bond network and a water channel located between the N- and P-side surfaces. However, a system for unidirectional proton-transport has not been experimentally identified. Here, an essentially identical X-ray structure for the two catalytic intermediates (P and F) of bovine CcO was determined at 1.8 Å resolution. A 1.70 Å Fe–O distance of the ferryl center could best be described as Fea34+ = O2−, not as Fea34+–OH−. The distance suggests an ∼800-cm−1 Raman stretching band. We found an interstitial water molecule that could trigger a rapid proton-coupled electron transfer from tyrosine-OH to the slowly forming Fea33+–O−–O−–CuB2+ state, preventing its detection, consistent with the unexpected Raman results. The H-pathway structures of both intermediates indicated that during proton-pumping from the hydrogen-bond network to the P-side, a transmembrane helix closes the water channel connecting the N-side with the hydrogen-bond network, facilitating unidirectional proton-pumping during the P-to-F transition.

Cell-surface signaling (CSS) in Gram-negative bacteria involves highly conserved regulatory pathways that optimize gene expression by transducing extracellular environmental signals to the cytoplasm via inner-membrane sigma regulators. The molecular details of ferric siderophore-mediated activation of the iron import machinery through a sigma regulator are unclear. Here, we present the 1.56 Å resolution structure of the periplasmic complex of the C-terminal CSS domain (CCSSD) of PupR, the sigma regulator in the Pseudomonas capeferrum pseudobactin BN7/8 transport system, and the N-terminal signaling domain (NTSD) of PupB, an outer-membrane TonB-dependent transducer. The structure revealed that the CCSSD consists of two subdomains: a juxta-membrane subdomain, which has a novel all-β-fold, followed by a secretin/TonB, short N-terminal subdomain at the C terminus of the CCSSD, a previously unobserved topological arrangement of this domain. Using affinity pulldown assays, isothermal titration calorimetry, and thermal denaturation CD spectroscopy, we show that both subdomains are required for binding the NTSD with micromolar affinity and that NTSD binding improves CCSSD stability. Our findings prompt us to present a revised model of CSS wherein the CCSSD:NTSD complex forms prior to ferric-siderophore binding. Upon siderophore binding, conformational changes in the CCSSD enable regulated intramembrane proteolysis of the sigma regulator, ultimately resulting in transcriptional regulation.

Knowledge of the molecular events in mitochondrial DNA (mtDNA) replication is crucial to understanding the origins of human disorders arising from mitochondrial dysfunction. Twinkle helicase is an essential component of mtDNA replication. Here, we employed atomic force microscopy imaging in air and liquids to visualize ring assembly, DNA binding, and unwinding activity of individual Twinkle hexamers at the single-molecule level. We observed that the Twinkle subunits self-assemble into hexamers and higher-order complexes that can switch between open and closed-ring configurations in the absence of DNA. Our analyses helped visualize Twinkle loading onto and unloading from DNA in an open-ringed configuration. They also revealed that closed-ring conformers bind and unwind several hundred base pairs of duplex DNA at an average rate of ∼240 bp/min. We found that the addition of mitochondrial single-stranded (ss) DNA–binding protein both influences the ways Twinkle loads onto defined DNA substrates and stabilizes the unwound ssDNA product, resulting in a ∼5-fold stimulation of the apparent DNA-unwinding rate. Mitochondrial ssDNA-binding protein also increased the estimated translocation processivity from 1750 to >9000 bp before helicase disassociation, suggesting that more than half of the mitochondrial genome could be unwound by Twinkle during a single DNA-binding event. The strategies used in this work provide a new platform to examine Twinkle disease variants and the core mtDNA replication machinery. They also offer an enhanced framework to investigate molecular mechanisms underlying deletion and depletion of the mitochondrial genome as observed in mitochondrial diseases.

The rapid emergence and dissemination of methicillin-resistant Staphylococcus aureus (MRSA) strains poses a major threat to public health. MRSA possesses an arsenal of secreted host-damaging virulence factors that mediate pathogenicity and blunt immune defenses. Panton–Valentine leukocidin (PVL) and α-toxin are exotoxins that create lytic pores in the host cell membrane. They are recognized as being important for the development of invasive MRSA infections and are thus potential targets for antivirulence therapies. Here, we report the high-resolution X-ray crystal structures of both PVL and α-toxin in their soluble, monomeric, and oligomeric membrane-inserted pore states in complex with n-tetradecylphosphocholine (C14PC). The structures revealed two evolutionarily conserved phosphatidylcholine-binding mechanisms and their roles in modulating host cell attachment, oligomer assembly, and membrane perforation. Moreover, we demonstrate that the soluble C14PC compound protects primary human immune cells in vitro against cytolysis by PVL and α-toxin and hence may serve as the basis for the development of an antivirulence agent for managing MRSA infections.

Much of our current knowledge of biological chemistry is founded in the structure-function relationship, whereby sequence determines structure that determines function. Thus, the discovery that a large fraction of the proteome is intrinsically disordered, while being functional, has revolutionized our understanding of proteins and raised new and interesting questions. Many intrinsically disordered proteins (IDPs) have been determined to undergo a disorder-to-order transition when recognizing their physiological partners, suggesting that their mechanisms of folding are intrinsically different from those observed in globular proteins. However, IDPs also follow some of the classic paradigms established for globular proteins, pointing to important similarities in their behavior. In this review, we compare and contrast the folding mechanisms of globular proteins with the emerging features of binding-induced folding of intrinsically disordered proteins. Specifically, whereas disorder-to-order transitions of intrinsically disordered proteins appear to follow rules of globular protein folding, such as the cooperative nature of the reaction, their folding pathways are remarkably more malleable, due to the heterogeneous nature of their folding nuclei, as probed by analysis of linear free-energy relationship plots. These insights have led to a new model for the disorder-to-order transition in IDPs termed “templated folding,” whereby the binding partner dictates distinct structural transitions en route to product, while ensuring a cooperative folding.

Formate oxidation to carbon dioxide is a key reaction in one-carbon compound metabolism, and its reverse reaction represents the first step in carbon assimilation in the acetogenic and methanogenic branches of many anaerobic organisms. The molybdenum-containing dehydrogenase FdsABG is a soluble NAD+-dependent formate dehydrogenase and a member of the NADH dehydrogenase superfamily. Here, we present the first structure of the FdsBG subcomplex of the cytosolic FdsABG formate dehydrogenase from the hydrogen-oxidizing bacterium Cupriavidus necator H16 both with and without bound NADH. The structures revealed that the two iron-sulfur clusters, Fe4S4 in FdsB and Fe2S2 in FdsG, are closer to the FMN than they are in other NADH dehydrogenases. Rapid kinetic studies and EPR measurements of rapid freeze-quenched samples of the NADH reduction of FdsBG identified a neutral flavin semiquinone, FMNH•, not previously observed to participate in NADH-mediated reduction of the FdsABG holoenzyme. We found that this semiquinone forms through the transfer of one electron from the fully reduced FMNH−, initially formed via NADH-mediated reduction, to the Fe2S2 cluster. This Fe2S2 cluster is not part of the on-path chain of iron-sulfur clusters connecting the FMN of FdsB with the active-site molybdenum center of FdsA. According to the NADH-bound structure, the nicotinamide ring stacks onto the re-face of the FMN. However, NADH binding significantly reduced the electron density for the isoalloxazine ring of FMN and induced a conformational change in residues of the FMN-binding pocket that display peptide-bond flipping upon NAD+ binding in proper NADH dehydrogenases.

The CRISPR/Cas9 nucleases have been widely applied for genome editing in various organisms. Cas9 nucleases complexed with a guide RNA (Cas9–gRNA) find their targets by scanning and interrogating the genomic DNA for sequences complementary to the gRNA. Recognition of the DNA target sequence requires a short protospacer adjacent motif (PAM) located outside this sequence. Given that the efficiency of target location may depend on the strength of interactions that promote target recognition, here we sought to compare affinities of different Cas9 nucleases for their cognate PAM sequences. To this end, we measured affinities of Cas9 nucleases from Streptococcus pyogenes, Staphylococcus aureus, and Francisella novicida complexed with guide RNAs (gRNAs) (SpCas9–gRNA, SaCas9–gRNA, and FnCas9–gRNA, respectively) and of three engineered SpCas9–gRNA variants with altered PAM specificities for short, PAM-containing DNA probes. We used a “beacon” assay that measures the relative affinities of DNA probes by determining their ability to competitively affect the rate of Cas9–gRNA binding to fluorescently labeled target DNA derivatives called “Cas9 beacons.” We observed significant differences in the affinities for cognate PAM sequences among the studied Cas9 enzymes. The relative affinities of SpCas9–gRNA and its engineered variants for canonical and suboptimal PAMs correlated with previous findings on the efficiency of these PAM sequences in genome editing. These findings suggest that high affinity of a Cas9 nuclease for its cognate PAM promotes higher genome-editing efficiency.

Carbon monoxide (CO) remains the most common cause of human poisoning. The consequences of CO poisoning include cardiac dysfunction, brain injury, and death. CO causes toxicity by binding to hemoglobin and by inhibiting mitochondrial cytochrome c oxidase (CcO), thereby decreasing oxygen delivery and inhibiting oxidative phosphorylation. We have recently developed a CO antidote based on human neuroglobin (Ngb-H64Q-CCC). This molecule enhances clearance of CO from red blood cells in vitro and in vivo. Herein, we tested whether Ngb-H64Q-CCC can also scavenge CO from CcO and attenuate CO-induced inhibition of mitochondrial respiration. Heart tissue from mice exposed to 3% CO exhibited a 42 ± 19% reduction in tissue respiration rate and a 33 ± 38% reduction in CcO activity compared with unexposed mice. Intravenous infusion of Ngb-H64Q-CCC restored respiration rates to that of control mice correlating with higher electron transport chain CcO activity in Ngb-H64Q-CCC–treated compared with PBS-treated, CO-poisoned mice. Further, using a Clark-type oxygen electrode, we measured isolated rat liver mitochondrial respiration in the presence and absence of saturating solutions of CO (160 μm) and nitric oxide (100 μm). Both CO and NO inhibited respiration, and treatment with Ngb-H64Q-CCC (100 and 50 μm, respectively) significantly reversed this inhibition. These results suggest that Ngb-H64Q-CCC mitigates CO toxicity by scavenging CO from carboxyhemoglobin, improving systemic oxygen delivery and reversing the inhibitory effects of CO on mitochondria. We conclude that Ngb-H64Q-CCC or other CO scavengers demonstrate potential as antidotes that reverse the clinical and molecular effects of CO poisoning.

Expert

Expert

Cytochrome c oxidase (CcO) reduces O2 to water, coupled with a proton-pumping process. The structure of the O2-reduction site of CcO contains two reducing equivalents, Fea32+ and CuB1+, and suggests that a peroxide-bound state (Fea33+–O−–O−–CuB2+) rather than an O2-bound state (Fea32+–O2) is the initial catalytic intermediate. Unexpectedly, however, resonance Raman spectroscopy results have shown that the initial intermediate is Fea32+–O2, whereas Fea33+–O−–O−–CuB2+ is undetectable. Based on X-ray structures of static noncatalytic CcO forms and mutation analyses for bovine CcO, a proton-pumping mechanism has been proposed. It involves a proton-conducting pathway (the H-pathway) comprising a tandem hydrogen-bond network and a water channel located between the N- and P-side surfaces. However, a system for unidirectional proton-transport has not been experimentally identified. Here, an essentially identical X-ray structure for the two catalytic intermediates (P and F) of bovine CcO was determined at 1.8 Å resolution. A 1.70 Å Fe–O distance of the ferryl center could best be described as Fea34+ = O2−, not as Fea34+–OH−. The distance suggests an ∼800-cm−1 Raman stretching band. We found an interstitial water molecule that could trigger a rapid proton-coupled electron transfer from tyrosine-OH to the slowly forming Fea33+–O−–O−–CuB2+ state, preventing its detection, consistent with the unexpected Raman results. The H-pathway structures of both intermediates indicated that during proton-pumping from the hydrogen-bond network to the P-side, a transmembrane helix closes the water channel connecting the N-side with the hydrogen-bond network, facilitating unidirectional proton-pumping during the P-to-F transition.

Kainate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are two major, closely related receptor subtypes in the glutamate ion channel family. Excessive activities of these receptors have been implicated in a number of central nervous system diseases. Designing potent and selective antagonists of these receptors, especially of kainate receptors, is useful for developing potential treatment strategies for these neurological diseases. Here, we report on two RNA aptamers designed to individually inhibit kainate and AMPA receptors. To improve the biostability of these aptamers, we also chemically modified these aptamers by substituting their 2'-OH group with 2'-fluorine. These 2'-fluoro aptamers, FB9s-b and FB9s-r, were markedly resistant to RNase-catalyzed degradation, with a half-life of ∼5 days in rat cerebrospinal fluid or serum-containing medium. Furthermore, FB9s-r blocked AMPA receptor activity. Aptamer FB9s-b selectively inhibited GluK1 and GluK2 kainate receptor subunits, and also GluK1/GluK5 and GluK2/GluK5 heteromeric kainate receptors with equal potency. This inhibitory profile makes FB9s-b a powerful template for developing tool molecules and drug candidates for treatment of neurological diseases involving excessive activities of the GluK1 and GluK2 subunits.

Publication Date: Apr 10 2020 The SEC will withdraw the existing approval order and the fund will become subject to the requirements of Rule 6c-11 and Nasdaq Rule 5704....

euromicron AG, a medium-sized technology group and expert on digital networking of business and production processes, held its Annual General Meeting 2019 in Frankfurt/Main on August 29, 2019. 42 percent of the share capital was represented. At the Annual General Meeting, the Executive Board reported on the operating performance in fiscal year 2018 and in the first half of 2019 and gave an outlook on the current fiscal year. One focus was on the implementation of the measures initiated to focus on and further develop the business model.

On this last Sunday of 2019, I wish every Hong Kong citizen a warm, peaceful and hopeful year 2020.

A New Year holds welcome promises of a fresh start and a new beginning. The New Year is also traditionally a time for planning, greeting, reminiscing as well as some soul and heart searching.

I believe that many of you would share my feeling that the year 2019 has been a year of unremitting shocks and turbulence to our community and our economy. Indeed, it has been a severely testing time for all in Hong Kong.

It all began with the introduction into the Legislative Council of the bill to amend the Fugitive Offenders Ordinance in April. Responding to strong public sentiment, the Government suspended all work on the bill in mid-June and declared its death in early July. On September 4, the Chief Executive announced the bill's withdrawal. This was done on October 23 when the Legislative Council resumed normal business.

Despite this, the public protests which began as largely peaceful and orderly marches in June soon got out of control. Unprecedented violence and reckless destruction became the norm. Radical protesters attacked police officers as well as police stations and facilities with petrol bombs, iron bars, bricks and chemicals. Some even used high-tension slingshots, bows and arrows. During the past six months or so, over 2,600 people were injured in the social unrest, including over 500 police officers.

Meanwhile, public infrastructure and transport including a cumulative total of 85 heavy rail stations and 62 light rail stations, as well as countless shops, restaurants and shopping malls had been repeatedly vandalised. More so, nearly 21,000 square metres of paving blocks from footpaths were ripped up and used as weapons to attack Police. Over 52,000 metres of roadside railing were removed and 740 sets of traffic lights destroyed.

Last month, masked protesters battered the Hung Hom Cross-Harbour Tunnel, shutting it down for two full weeks. This vital city artery normally carries 110,000 vehicles a day, accounting for some 43% of the daily cross-harbour vehicular flow. It took a total of 800 government staff and contractor's workers some 100 hours to carry out emergency repair round-the-clock before the tunnel could be reopened. At the same time, nearby Polytechnic University was overrun by radical protesters. The same happened to the Chinese University.

Apart from recklessly damaging our universities, violent protesters turned the two campuses into arsenals on a frightening scale. When the last of the protesters finally left the universities, Police seized altogether nearly 8,000 petrol bombs plus numerous explosives, hundreds of bottles of corrosive liquid and weapons of all sorts.

This level of premeditated and organised destruction and violence could hardly be tolerated in any country or economy that upholds the rule of law. Hong Kong, I am proud to say, is among those economies that believe passionately in the primacy of rule of law. It safeguards our economy, our community, our families and our way of life.

In fact, the rule of law is among Hong Kong's much cherished core values, alongside our fiercely independent judiciary, clean government, level playing field for business and enviable freedoms. These freedoms, as enshrined in the Basic Law and the Hong Kong Bill of Rights Ordinance, include freedom of speech, of the press and free flow of information; freedom of association and assembly; free trade and free port; free flow of capital; freely convertible currency; freedom of religious belief and free education. We have also been the freest economy in the world continuously for 25 years. The unique "one country, two systems" formula has been functioning well and we enjoy the best of both worlds.

Despite the recent social unrest which has affected our economy and labour market, Hong Kong's institutional strengths remain robust and intact. Our fundamentals stay sound and strong. We still enjoy a high rating in various areas by international think tanks and agencies. Allow me to say that whilst Hong Kong may not have the full semblance of Western democracy, we do enjoy for a very long time the full substance of real freedom which underpins Hong Kong's success.

Over the past six months, most of the requests for public meetings, processions and protests were given the greenlight by Police. During these public events, be it small or large, Police had dutifully facilitated and ensured the safety of protesters and other road users. When the requests were not approved, it was generally a decision made in the hopes of preventing violence, ensuring peace and public order, as our society has every right to expect of its police and its government.

On November 24, we witnessed a peaceful and orderly District Council Election with a record high turnout and voting rates. My colleagues and I are looking forward to working with all new District Council members. We also look forward to expanding our dialogue with the community. While we will continue to engage different sectors of society through our usual channels, the Government will broaden and rejuvenate our communication with the public. Less than two weeks ago and after the one by the Chief Executive in September, my Principal Official colleagues have started a dialogue with the public through Facebook live. You will certainly see more of us listening and responding to people's views and concerns on these and other communication channels in the coming year.

We are also establishing an Independent Review Committee comprising experts and community leaders. The committee will look into the causes and full circumstances of the social unrest and probe into Hong Kong's deep-seated social conflicts, from affordable housing, land supply, wealth gap, upward social mobility and opportunities for our young people to social justice. The committee will recommend ways to address the real and long-entrenched community concerns that underlie the discord.

Meanwhile, our economy is inevitably affected by the twin blows of social unrest and the trade dispute between the United States and the Mainland. Businesses and people of Hong Kong are yearning for the restoration of peace and order soonest possible, and the recovery of our economy.

In response, the Government has launched four rounds of relief measures since August. These added up to more than $25 billion. A number of the measures which will benefit grassroots families and small and medium enterprises will be implemented at the beginning of the New Year.

These relief measures would not solve our economic problems. Yet, they could help businesses and people of Hong Kong stay afloat while we strive to heal our divided community and battered economy.

There are deep-seated issues that we must acknowledge and resolve if we are to end the prolonged social unrest that has shaken the familiar Hong Kong which we all love and cherish. We must be patient and perseverant in helping our city to heal, one step at a time.

The past six months have been tough for us, but we will soldier on. Hong Kong is a remarkably resilient and resourceful international city with a strong can-do spirit. We have a New Year waiting for us. We have new and expanded channels of communication opened up for us. We expect the first report of the Independent Police Complaints Council to come out soon. And we have research and concrete recommendations of the Independent Review Committee ahead of us. Working together, I am confident that we can rebuild, reclaim and rejuvenate the remarkably resilient spirit of Hong Kong.

On this note, I wish all of you a New Year blessed with peace, harmony and goodwill.

Chief Secretary Matthew Cheung gave these remarks on RTHK's "Letter to Hong Kong" programme aired on December 29.

Belinda S. O’Connell
Aug 1, 2001; 14:
Articles

The partnership will join hands with four UK startups as it hopes to reduce plastic waste as part of its retail tech initiative, JLAB

17 individuals in the mathematical sciences are among the 126 new members and foreign associates elected to the National Academy of Sciences (NAS) in 2020.

Members: Ivet Bahar, University of Pittsburgh School of Medicine; Abhijit Banerjee, Massachusetts Institute of Technology; Gerard Ben Arous, Courant Institute of Mathematical Sciences, New York University; Bonnie Berger, Massachusetts Institute of Technology; Laura G. DeMarco, Northwestern University; Ronald Fagin, IBM Almaden Research Center; Katherine Freese, The University of Texas at Austin; Dennis Gaitsgory, Harvard University; Robert L. Griess, University of Michigan, Ann Arbor; Jacob Lurie, Institute for Advanced Study; Terence T. Hwa, University of California, San Diego; Wilfried Schmid, Harvard University; Jeffrey D. Ullman, Stanford University; Lai-Sang Young, Courant Institute of Mathematical Sciences, New York University; and Ofer Zeitouni, Weizmann Institute of Science; Foreign Associates: Yoav Benjamini, Tel Aviv University (Israel) and Jürg Fröhlich, ETH Zurich (Switzerland). Berger, DeMarco, Griess, Schmid, and Zeitouni are members of the AMS and Fellows of the AMS. Fagin is a member of the AMS.

The NAS recognizes achievement in science by election to membership, and—along with the National Academy of Engineering and the National Academy of Medicine—provides science, engineering, and health policy advice to the federal government and other organizations. See the full list of this year's honorees. (Image courtesy of the National Academy of Sciences.)