l-Hydroxyproline (l-Hyp) is a nonstandard amino acid that is present in certain proteins, in some antibiotics and in the cell-wall components of plants. l-Hyp is the product of the post-translational modification of protein prolines by prolyl hydroxylase enzymes, and the isomers trans-3-hydroxy-l-proline (T3LHyp) and trans-4-hydroxy-l-proline (T4LHyp) are major components of mammalian collagen. T4LHyp follows two distinct degradation pathways in bacteria and mammals, while T3LHyp is metabolized by a two-step metabolic pathway that is conserved in bacteria and mammals, which involves a T3LHyp dehydratase and a Δ1-pyrroline-2-carboxylate (Pyr2C) reductase. In order to shed light on the structure and catalysis of the enzyme involved in the second step of the T3LHyp degradation pathway, the crystal structure of Pyr2C reductase from the archaeon Thermococcus litoralis DSM 5473 complexed with NADH and l-proline is presented. The model allows the mapping of the residues involved in cofactor and product binding and represents a valid model for rationalizing the catalysis of Pyr2C reductases.

Scott J. Neal, Qingxiang Zhou, and Francesca Pignoni

The specification of organs, tissues and cell types results from cell fate restrictions enacted by nuclear transcription factors under the control of conserved signaling pathways. The progenitor epithelium of the Drosophila compound eye, the eye imaginal disc, is a premier model for the study of such processes. Early in development, apposing cells of the eye disc are established as either retinal progenitors or support cells of the peripodial epithelium (PE), in a process whose genetic and mechanistic determinants are poorly understood. We have identified Protein Phosphatase 2A (PP2A), and specifically a STRIPAK-PP2A complex that includes the scaffolding and substrate-specificity components Cka, Strip and SLMAP, as a critical player in the retina-PE fate choice. We show that these factors suppress ectopic retina formation in the presumptive PE and do so via the Hippo signaling axis. STRIPAK-PP2A negatively regulates Hpo kinase, and consequently its substrate Wts, to release the transcriptional co-activator Yki into the nucleus. Thus, a modular higher-order PP2A complex refines the activity of this general phosphatase to act in a precise specification of cell fate.

Archan Chakraborty, Wei-Cheng Lin, Yu-Tsun Lin, Kuang-Jing Huang, Pei-Yu Wang, Yi-Feng Chang, Hsiang-Iu Wang, Kung-Ting Ma, Chun-Yen Wang, Xuan-Rong Huang, Yen-Hsien Lee, Bi-Chang Chen, Ya-Ju Hsieh, Kun-Yi Chien, Tzu-Yang Lin, Ji-Long Liu, Li-Ying Sung, Jau-Song Yu, Yu-Sun Chang, and Li-Mei Pai

Under metabolic stress, cellular components can assemble into distinct membraneless organelles for adaptation. One such example is cytidine 5'-triphosphate synthase (CTPS), which forms filamentous structures under glutamine deprivation. We have previously demonstrated that histidine (His)-mediated methylation regulates the formation of CTPS filaments to suppress enzymatic activity and preserve the CTPS protein under Gln deprivation, which promotes cancer cell growth after stress alleviation. However, it remains unclear where and how these enigmatic structures are assembled. Using CTPS-APEX2-mediated in vivo proximity labeling, we found that SNAP29 regulates the spatiotemporal filament assembly of CTPS along the cytokeratin network in a keratin 8 (KRT8)-dependent manner. Knockdown of synaptosome-associated protein 29 (SNAP29) interfered with assembly and relaxed the filament-induced suppression of CTPS enzymatic activity. Furthermore, APEX2 proximity labeling of keratin 18 (KRT18) revealed a spatiotemporal association of SNAP29 with cytokeratin in response to stress. Super-resolution imaging suggests that during CTPS filament formation, SNAP29 interacts with CTPS along the cytokeratin network. This study links the cytokeratin network to the regulation of metabolism by compartmentalization of metabolic enzymes during nutrient deprivation.

Christian Renz, Veronique Albanese, Vera Tröster, Thomas K. Albert, Olivier Santt, Susan C. Jacobs, Anton Khmelinskii, Sebastien Leon, and Helle D. Ulrich

Polyubiquitin chains linked via lysine (K) 63 play an important role in endocytosis and membrane trafficking. Their primary source is the ubiquitin protein ligase (E3) Rsp5/NEDD4, which acts as a key regulator of membrane protein sorting. The heterodimeric ubiquitin-conjugating enzyme (E2), Ubc13-Mms2, catalyses K63-specific polyubiquitylation in genome maintenance and inflammatory signalling. In budding yeast, the only ubiquitin protein ligase (E3) known to cooperate with Ubc13-Mms2 so far is a nuclear RING finger protein, Rad5, involved in the replication of damaged DNA. We now report a contribution of Ubc13-Mms2 to the sorting of membrane proteins to the yeast vacuole via the multivesicular body (MVB) pathway. In this context, Ubc13-Mms2 cooperates with Pib1, a FYVE-RING finger protein associated with internal membranes. Moreover, we identified a family of membrane-associated FYVE-(type)-RING finger proteins as cognate E3s for Ubc13-Mms2 in several species, and genetic analysis indicates that the contribution of Ubc13-Mms2 to membrane trafficking in budding yeast goes beyond its cooperation with Pib1. Thus, our results widely implicate Ubc13-Mms2 as an Rsp5-independent source of K63-linked polyubiquitin chains in the regulation of membrane protein sorting.

Kristina Drizyte-Miller, Jing Chen, Hong Cao, Micah B. Schott, and Mark A. McNiven

Epithelial cells such as liver-resident hepatocytes rely heavily on the Rab family of small GTPases to perform membrane trafficking events that dictate cell physiology and metabolism. Not surprisingly, disruption of several Rabs can manifest in metabolic diseases or cancer. Rab32 is expressed in many secretory epithelial cells but its role in cellular metabolism is virtually unknown. In this study, we find that Rab32 associates with lysosomes and regulates proliferation and cell size of Hep3B hepatoma and HeLa cells. Specifically, we identify that Rab32 supports mTORC1 signaling under basal and amino acid stimulated conditions. Consistent with inhibited mTORC1, an increase in nuclear TFEB localization and lysosome biogenesis is also observed in Rab32-depleted cells. Finally, we find that Rab32 interacts with mTOR kinase and that loss of Rab32 reduces the association of mTOR and mTORC1 pathway proteins with lysosomes, suggesting that Rab32 regulates lysosomal mTOR trafficking. In summary, these findings suggest that Rab32 functions as a novel regulator of cellular metabolism through supporting mTORC1 signaling.

Juan Martin D'Ambrosio, Veronique Albanese, Nicolas-Frederic Lipp, Lucile Fleuriot, Delphine Debayle, Guillaume Drin, and Alenka Copic

Osh6 and Osh7 are lipid transfer proteins (LTPs) that move phosphatidylserine (PS) from the endoplasmic reticulum (ER) to the plasma membrane (PM). High PS level at the PM is key for many cellular functions. Intriguingly, Osh6/7 localize to ER-PM contact sites, although they lack membrane-targeting motifs, in contrast to multidomain LTPs that both bridge membranes and convey lipids. We show that Osh6 localization to contact sites depends on its interaction with the cytosolic tail of the ER-PM tether Ist2, a homologue of TMEM16 proteins. We identify a motif in the Ist2 tail, conserved in yeasts, as the Osh6-binding region, and we map an Ist2-binding surface on Osh6. Mutations in the Ist2 tail phenocopy osh6 osh7 deletion: they decrease cellular PS levels, and block PS transport to the PM. Our study unveils an unexpected partnership between a TMEM16-like protein and a soluble LTP, which together mediate lipid transport at contact sites.

Julian Chollet, Alexander Dünkler, Anne Bäuerle, Laura Vivero-Pol, Medhanie A. Mulaw, Thomas Gronemeyer, and Nils Johnsson

Yeast cells select the position of their new bud at the beginning of each cell cycle. The recruitment of the septins to this prospective bud site is one of the critical events in a complex assembly pathway that culminates in the outgrowth of a new daughter cell. Hereby, the septin-rods follow the high concentration of Cdc42_GTP that is generated by the focused localization of its GEF Cdc24. We show that shortly before budding Cdc24 not only activates Cdc42 but also transiently interacts with Cdc11, the septin subunit that caps both ends of the septin rods. Mutations in Cdc24 reducing the affinity to Cdc11 impair septin recruitment and decrease the stability of the polarity patch. The interaction between septins and Cdc24 thus reinforces bud assembly at sites where septin structures are formed. Once the septins polymerize into the ring, Cdc24 is found at the cortex of the bud and directs its further outgrowth from this position.

Mei Wang, Luping Yu, Shu Wang, Fan Yang, Min Wang, Lufan Li, and Xin Wu

RNA-binding protein LIN28A is required for maintaining tissue homeostasis, including the reproductive system, but the underlying mechanisms on how LIN28A regulates germline progenitors remain unclear. Here, we dissected LIN28A-binding targets using high-throughput sequencing of RNAs isolated by crosslinking immunoprecipitation (HITS-CLIP) in the mouse testes. LIN28A preferentially binds to CDS or 3'UTR regions through these sites with GGAG(A) sequences enriched within mRNAs. Further investigation of Lin28a null mouse testes indicated that meiosis-associated mRNAs mediated by LIN28A were differentially expressed. Next, ribosome profiling revealed that the mRNA levels of these targets were significantly reduced in polysome fractions, and their protein expression levels decreased in the Lin28a null mouse testes, even when meiotic arrest in null mouse testes was not apparent. Collectively, these findings provide a set of binding targets that are regulated by LIN28A, which may potentially be the mechanism for the prominent role of LIN28A in regulating mammalian undifferentiated spermatogonia fates and male fertility.

Richard Wunderman is managing editor of the Bulletin of the Global Volcanism Network and a geologist in the Division of Mineral Sciences at the Smithsonian’s […]

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The last time Earth experienced both ice sheets and carbon dioxide levels within the range predicted for this century was a period of major sea […]

The post What the Ancient CO2 Record May Mean for Future Climate Change appeared first on Smithsonian Insider.

The Jamaican golden swallow was last seen in 1982. From 1994 to 2012, Smithsonian ornithologist Gary Graves combed the island of Jamaica to document several […]

The post After a nearly 20-year search, this Jamaican bird is probably extinct appeared first on Smithsonian Insider.

Seven corrections are made and several supplementary equations are added to the article by Yoshimura [Acta Cryst. (2015), A71, 368–381].

"The Antarctic Treaty Summit: Science-Policy Interactions in International Governance" will be convened at the Smithsonian Institution, National Museum of Natural History in Washington, DC from Nov. 30 to Dec. 3 2009. More information on this event can be found at the Web site: www.atsummit50.aq/

To assess legacy lessons about managing nearly 10% of the Earth "for peaceful purposes only"

Find out how you can be involved:

www.atsummit50.aq

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Eyjafjallajökull's eruption may be a hassle if you had any transatlantic flights planned this summer. For scientists, however, volcanic eruptions are the only way they can obtain samples from deep within the Earth to learn more about our planet, its formation, and its ongoing evolution. Smithsonian Geologist Liz Cottrell helps put this recent eruption into perspective.

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The three male cheetahs that left the Zoo's D.C. campus in 2009 returned in November and are now on exhibit. The five-and-a-half-year-old brothers―Draco, Granger, and Zabini, named after characters in the Harry Potter stories―have been living at the Zoo's Smithsonian Conservation Biology Institute's Cheetah Science Facility in Front Royal, Virginia.

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The post Many years of research are celebrated in the December 2010 birth of two cheetah cubs at the Smithsonian Conservation Biology Institute appeared first on Smithsonian Insider.

National Zoo Veterinarian Katharine Hope treats about 2,000 animals from 400 different species. She and her colleagues care for a variety of animals, from small baby flamingos to adult Asian elephants, so there's no such thing as an average day.

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The post Smithsonian geologist Liz Cottrell discusses the March 11, 2011 Japan earthquake and its mechanics appeared first on Smithsonian Insider.

Paleoecologist Conrad Labandeira travels to the Karoo Basin of South Africa to find leaf fossils from the Permian-Triassic boundary, the time of the Earth's largest mass extinction. What can bug bites on leaves tell us about our own uncertain times?

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The post The Space Shuttle Discovery, mounted atop a 747 jet, is delivered to the Smithsonian on April 17, 2012 appeared first on Smithsonian Insider.

The post Creating a dictionary: Gabriela Pérez Báez, Curator of Linguistics appeared first on Smithsonian Insider.

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The post Smithsonian conservators open 2001 Jim Thorpe Wheaties Box from the Smithsonian’s National Museum of the American Indian appeared first on Smithsonian Insider.

Silent black & white archival film clip from "Japan: Promotional and Theatrical Footage, ca. 1927". The full film, which is 17 minutes long, includes segments from what are believed to be a theatrical film, a promotional film and, possibly, amateur film - all of unknown origin.

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One of Italy’s greatest treasures, Leonardo da Vinci’s Codex on the Flight of Birds, will be exhibited at the National Air and Space Museum from […]

The post da Vinci’s “Codex on the Flight of Birds” will be on view at Air and Space Museum, Sept. 13-Oct. 22. appeared first on Smithsonian Insider.

The National Air and Space Museum’s 2014 Trophy Award Winner for Current Achievement goes to the Dawn Flight Team. The Dawn team has successfully performed […]

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For the first time in nearly 22 years, the Spirit of St. Louis is lowered onto the floor of the Boeing Milestones of Flight Hall. […]

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“The Outwin 2016: American Portraiture Today” exhibition is on view at the Smithsonian’s National Portrait Gallery from March 12, 2016 – January 8, 2017. The Outwin […]

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Jennifer Trask engages nature as both medium and subject matter, combining unexpected materials such as bone, vertebrae, butterfly wings, resin, metal, and antique frame fragments […]

The post Jennifer Trask – Visions and Revisions: Renwick Invitational 2016 appeared first on Smithsonian Insider.

Steven Young Lee blends Eastern and Western traditions with anachronistic, often playful imagery and striking pattern in his porcelain works. His process allows the clay […]

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As the world prepares to celebrate Global Tiger Day this Saturday, July 29, Great Cats keepers at the Smithsonian’s National Zoo have some big news […]

The post 2-week-old Sumatran tiger cub at National Zoo appeared first on Smithsonian Insider.

Highlights of the year 2017 Freer Gallery of Art and Arthur M. Sackler Gallery

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