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Kai Cai, Ronnie O Frederick, Hesam Dashti, John L Markley
Cysteine desulfurase plays a central role in mitochondrial iron-sulfur cluster biogenesis by generating sulfur through the conversion of L-cysteine to L-alanine and by serving as the platform for assembling other components of the biosynthetic machinery, including ISCU, frataxin, and ferredoxin. The human mitochondrial cysteine desulfurase complex consists of two copies each of NFS1, ISD11, and acyl carrier protein. We describe results from chemical crosslinking coupled with tandem mass spectrometry and small-angle X-ray scattering studies that are consistent with a closed NFS1 dimer rather than an open one for both the cysteine desulfurase-ISCU and cysteine desulfurase-ISCU-frataxin complexes...
June 8, 2018: Structure
Sanjay Mishra, Shane A Chandler, Dewight Williams, Derek P Claxton, Hanane A Koteiche, Phoebe L Stewart, Justin L P Benesch, Hassane S Mchaourab
Small heat-shock proteins (sHSPs) are molecular chaperones that bind partially and globally unfolded states of their client proteins. Previously, we discovered that the archaeal Hsp16.5, which forms ordered and symmetric 24-subunit oligomers, can be engineered to transition to an ordered and symmetric 48-subunit oligomer by insertion of a peptide from human HspB1 (Hsp27). Here, we uncovered the existence of an array of oligomeric states (30-38 subunits) that can be populated as a consequence of altering the sequence and length of the inserted peptide...
June 5, 2018: Structure
Shawn Xiong, Kristina Lorenzen, Amber L Couzens, Catherine M Templeton, Dushyandi Rajendran, Daniel Y L Mao, Yu-Chi Juang, David Chiovitti, Igor Kurinov, Sebastian Guettler, Anne-Claude Gingras, Frank Sicheri
The human NDR family kinases control diverse aspects of cell growth, and are regulated through phosphorylation and association with scaffolds such as MOB1. Here, we report the crystal structure of the human NDR1 kinase domain in its non-phosphorylated state, revealing a fully resolved atypically long activation segment that blocks substrate binding and stabilizes a non-productive position of helix αC. Consistent with an auto-inhibitory function, mutations within the activation segment of NDR1 dramatically enhance in vitro kinase activity...
June 1, 2018: Structure
Ana Monica Nunes, Conceição A S A Minetti, David P Remeta, Jean Baum
Integrin receptors bind collagen via metal-mediated interactions that are modulated by magnesium (Mg2+ ) levels in the extracellular matrix. Nuclear magnetic resonance-based relaxation experiments, isothermal titration calorimetry, and adhesion assays reveal that Mg2+ functions as both a structural anchor and dynamic switch of the α1 β1 integrin I domain (α1 I). Specifically, Mg2+ binding activates micro- to millisecond timescale motions of residues distal to the binding site, particularly those surrounding the salt bridge at helix 7 and near the metal ion-dependent adhesion site...
May 31, 2018: Structure
Madhumati Sevvana, Feng Long, Andrew S Miller, Thomas Klose, Geeta Buda, Lei Sun, Richard J Kuhn, Michael G Rossmann
Among the several arthropod-borne human flaviviral diseases, the recent outbreak of Zika virus (ZIKV) has caused devastating birth defects and neurological disorders, challenging the world with another major public health concern. We report here the refined structure of the mature ZIKV at a resolution of 3.1 Å as determined by cryo-electron microscopic single-particle reconstruction. The improvement in the resolution, compared with previous enveloped virus structures, was the result of optimized virus preparation methods and data processing techniques...
May 29, 2018: Structure
Inokentijs Josts, Julius Nitsche, Selma Maric, Haydyn D Mertens, Martine Moulin, Michael Haertlein, Sylvain Prevost, Dmitri I Svergun, Sebastian Busch, V Trevor Forsyth, Henning Tidow
Structural studies of integral membrane proteins (IMPs) are challenging, as many of them are inactive or insoluble in the absence of a lipid environment. Here, we describe an approach making use of fractionally deuterium labeled "stealth carrier" nanodiscs that are effectively invisible to low-resolution neutron diffraction and enable structural studies of IMPs in a lipidic native-like solution environment. We illustrate the potential of the method in a joint small-angle neutron scattering (SANS) and X-ray scattering (SAXS) study of the ATP-binding cassette (ABC) transporter protein MsbA solubilized in the stealth nanodiscs...
May 28, 2018: Structure
Mehmet Ali Öztürk, Vlad Cojocaru, Rebecca C Wade
There is renewed interest in linker histone (LH)-nucleosome binding and how LHs influence eukaryotic DNA compaction. For a long time, the goal was to uncover "the structure of the chromatosome," but recent studies of LH-nucleosome complexes have revealed an ensemble of structures. Notably, the reconstituted LH-nucleosome complexes used in experiments rarely correspond to the sequence combinations present in organisms. For a full understanding of the determinants of the distribution of the chromatosome structural ensemble, studies must include a complete description of the sequences and experimental conditions used, and be designed to enable systematic evaluation of sequence and environmental effects...
May 28, 2018: Structure
Grant M Shoffner, Ruixuan Wang, Elaine Podell, Thomas R Cech, Feng Guo
Crystallography is a major technique for determining large RNA structures. Obtaining diffraction-quality crystals has been the bottleneck. Although several RNA crystallization methods have been developed, the field strongly needs additional approaches. Here we invented an in crystallo selection strategy for identifying mutations that enhance a target RNA's crystallizability. The strategy includes constructing an RNA pool containing random mutations, obtaining crystals, and amplifying the sequences enriched by crystallization...
May 28, 2018: Structure
Nick Darvill, David J Dubois, Sarah L Rouse, Pierre-Mehdi Hammoudi, Tom Blake, Stefi Benjamin, Bing Liu, Dominique Soldati-Favre, Steve Matthews
Plasmodium falciparum and Toxoplasma gondii are obligate intracellular parasites that belong to the phylum of Apicomplexa and cause major human diseases. Their access to an intracellular lifestyle is reliant on the coordinated release of proteins from the specialized apical organelles called micronemes and rhoptries. A specific phosphatidic acid effector, the acylated pleckstrin homology domain-containing protein (APH) plays a central role in microneme exocytosis and thus is essential for motility, cell entry, and egress...
May 23, 2018: Structure
Alvin Yu, Albert Y Lau
At central nervous system synapses, agonist binding to postsynaptic ionotropic glutamate receptors (iGluRs) results in signaling between neurons. N-Methyl-D-aspartic acid (NMDA) receptors are a unique family of iGluRs that activate in response to the concurrent binding of glutamate and glycine. Here, we investigate the process of agonist binding to the GluN2A (glutamate binding) and GluN1 (glycine binding) NMDA receptor subtypes using long-timescale unbiased molecular dynamics simulations. We find that positively charged residues on the surface of the GluN2A ligand-binding domain (LBD) assist glutamate binding via a "guided-diffusion" mechanism, similar in fashion to glutamate binding to the GluA2 LBD of AMPA receptors...
May 23, 2018: Structure
Matthieu Chavent, Dimple Karia, Antreas C Kalli, Jan Domański, Anna L Duncan, George Hedger, Phillip J Stansfeld, Elena Seiradake, E Yvonne Jones, Mark S P Sansom
EphA2 is a member of the receptor tyrosine kinase family. Interactions of the cytoplasmic region of EphA2 with the cell membrane are functionally important and yet remain incompletely characterized. Molecular dynamics simulations combined with biochemical studies reveal the interactions of the transmembrane, juxtamembrane (JM), and kinase domains with the membrane. We describe how the kinase domain is oriented relative to the membrane and how the JM region can modulate this interaction. We highlight the role of phosphatidylinositol phosphates (PIPs) in mediating the interaction of the kinase domain with the membrane and, conversely, how positively charged patches at the kinase surface and in the JM region induce the formation of nanoclusters of PIP molecules in the membrane...
May 22, 2018: Structure
Jose K James, Douglas H Pike, I John Khan, Vikas Nanda
To what extent do structural and biophysical features of food allergen proteins distinguish them from other proteins in our diet? Invertebrate tropomyosins (Tpms) as a class are considered "pan-allergens," inducing food allergy to shellfish and respiratory allergy to dust mites. Vertebrate Tpms are not known to elicit allergy or cross-reactivity, despite their high structural similarity and sequence identity to invertebrate homologs. We expect allergens are sufficiently stable against gastrointestinal proteases to survive for immune sensitization in the intestines, and that proteolytic stability will correlate with thermodynamic stability...
May 22, 2018: Structure
Nicholas P Stone, Brendan J Hilbert, Daniel Hidalgo, Kevin T Halloran, Jooyoung Lee, Erik J Sontheimer, Brian A Kelch
Virus capsids are protein shells that protect the viral genome from environmental assaults, while maintaining the high internal pressure of the tightly packaged genome. To elucidate how capsids maintain stability under harsh conditions, we investigated the capsid components of the hyperthermophilic phage P74-26. We determined the structure of capsid protein gp87 and show that it has the same fold as decoration proteins in many other phages, despite lacking significant sequence homology. We also find that gp87 is significantly more stable than mesophilic homologs...
April 26, 2018: Structure
Roland G Huber, Nils A Berglund, Vasileios Kargas, Jan K Marzinek, Daniel A Holdbrook, Syma Khalid, Thomas J Piggot, Artur Schmidtchen, Peter J Bond
The Gram-negative bacterial outer membrane contains lipopolysaccharide, which potently stimulates the mammalian innate immune response. This involves a relay of specialized complexes culminating in transfer of lipopolysaccharide from CD14 to Toll-like receptor 4 (TLR4) and its co-receptor MD-2 on the cell surface, leading to activation of downstream inflammatory responses. In this study we develop computational models to trace the TLR4 cascade in near-atomic detail. We demonstrate through rigorous thermodynamic calculations that lipopolysaccharide molecules traversing the receptor cascade fall into a thermodynamic funnel...
April 25, 2018: Structure
Leah Gottlieb, Ronen Marmorstein
Co-translational N-terminal protein acetylation regulates many protein functions including degradation, folding, interprotein interactions, and targeting. Human NatA (hNatA), one of six conserved metazoan N-terminal acetyltransferases, contains Naa10 catalytic and Naa15 auxiliary subunits, and associates with the intrinsically disordered Huntingtin yeast two-hybrid protein K (HYPK). We report on the crystal structures of hNatA and hNatA/HYPK, and associated biochemical and enzymatic analyses. We demonstrate that hNatA contains unique features: a stabilizing inositol hexaphosphate (IP6 ) molecule and a metazoan-specific Naa15 domain that mediates high-affinity HYPK binding...
April 23, 2018: Structure
Soumya G Remesh, Anthony A Armstrong, Andrew D Mahan, Jinquan Luo, Michal Hammel
Fragment crystallizable (Fc) region of immunoglobulin G (IgG) antibody binds to specific Fc receptors (FcγRs) to control antibody effector functions. Currently, engineered specific Fc-FcγR interactions are validated with a static conformation derived from the crystal structure. However, computational evidence suggests that the conformational variability of Fcs plays an important role in receptor recognition. Here we elucidate Fc flexibility of IgG1, IgG2, and IgG1 Fc with mutations (M255Y/S257T/T259E) in solution by small-angle X-ray scattering (SAXS)...
April 18, 2018: Structure
Steven R Van Doren
Bacterial pathogens can switch signaling by sensing threonine phosphorylation. In this issue of Structure, Heinkel et al. (2018) report novel rearrangements linking threonine phosphorylation to tandem forkhead-associated (FHA) domains from an ATP-binding cassette (ABC) transporter. The resulting associations probably regulate oligomerization and transport in Mycoplasma tuberculosis.
July 3, 2018: Structure
Johannes Thoma, Yang Sun, Noah Ritzmann, Daniel J Müller
The core component BamA of the β barrel assembly machinery (BAM) adopts several conformations, which are thought to facilitate the insertion and folding of β barrel proteins into the bacterial outer membrane. Which factors alter the stability of these conformations remains to be quantified. Here, we apply single-molecule force spectroscopy to characterize the mechanical properties of BamA from Escherichia coli. In contrast to the N-terminal periplasmic polypeptide-transport-associated (POTRA) domains, the C-terminal transmembrane β barrel domain of BamA is mechanically much more stable...
July 3, 2018: Structure
Florian Heinkel, Leo Shen, Melissa Richard-Greenblatt, Mark Okon, Jennifer M Bui, Christine L Gee, Laurie M Gay, Tom Alber, Yossef Av-Gay, Jörg Gsponer, Lawrence P McIntosh
The Mycobacterium tuberculosis ATP-binding cassette transporter Rv1747 is a putative exporter of cell wall biosynthesis intermediates. Rv1747 has a cytoplasmic regulatory module consisting of two pThr-interacting Forkhead-associated (FHA) domains connected by a conformationally disordered linker with two phospho-acceptor threonines (pThr). The structures of FHA-1 and FHA-2 were determined by X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy, respectively. Relative to the canonical 11-strand β-sandwich FHA domain fold of FHA-1, FHA-2 is circularly permuted and lacking one β-strand...
July 3, 2018: Structure
Bernhard Rupp
The almost universally required "Table 1," summarizing data-collection and data-processing statistics, has in its present form outlived its usefulness in almost all publications of biomolecular crystal structure reports. Information contained in "Table 1" is insufficient to evaluate or repeat the experiment; is redundant with information extractable from deposited diffraction data; and includes data items whose meaning is under increased scrutiny in the crystallographic community. Direct and consistent extraction and analysis of data quality metrics from preferably unmerged intensity data with graphical presentation of reciprocal space features, including impact on map and model features, should replace "Table 1...
July 3, 2018: Structure
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