Journal of Molecular Biology

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  • Editorial Board
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8









    Categories: Journal Articles
  • Contents List
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8









    Categories: Journal Articles
  • A Novel Allosteric Mechanism on Protein–DNA Interactions underlying the Phosphorylation-Dependent Regulation of Ets1 Target Gene Expressions
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8

    Author(s): Masaaki Shiina , Keisuke Hamada , Taiko Inoue-Bungo , Mariko Shimamura , Akiko Uchiyama , Shiho Baba , Ko Sato , Masaki Yamamoto , Kazuhiro Ogata

    Cooperative assemblies of transcription factors (TFs) on target gene enhancers coordinate cell proliferation, fate specification, and differentiation through precise and complicated transcriptional mechanisms. Chemical modifications, such as phosphorylation, of TFs induced by cell signaling further modulate the dynamic cooperativity of TFs. In this study, we found that various Ets1-containing TF–DNA complexes respond differently to calcium-induced phosphorylation of Ets1, which is known to inhibit Ets1–DNA binding. Crystallographic analysis of a complex comprising Ets1, Runx1, and CBFβ at the TCRα enhancer revealed that Ets1 acquires robust binding stability in the Runx1 and DNA-complexed state, via allosteric mechanisms. This allows phosphorylated Ets1 to be retained at the TCRα enhancer with Runx1, in contrast to other Ets1 target gene enhancers including mb-1 and stromelysin-1. This study provides a structure-based model for cell-signaling-dependent regulation of target genes, mediated via chemical modification of TFs.
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    Categories: Journal Articles
  • Multiscale Modeling of a Conditionally Disordered pH-Sensing Chaperone
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8

    Author(s): Logan S. Ahlstrom , Sean M. Law , Alex Dickson , Charles L. Brooks III

    The pH-sensing chaperone HdeA promotes the survival of enteropathogenic bacteria during transit through the harshly acidic environment of the mammalian stomach. At low pH, HdeA transitions from an inactive, folded, dimer to chaperone-active, disordered, monomers to protect against the acid-induced aggregation of periplasmic proteins. Toward achieving a detailed mechanistic understanding of the pH response of HdeA, we develop a multiscale modeling approach to capture its pH-dependent thermodynamics. Our approach combines pK a (logarithmic acid dissociation constant) calculations from all-atom constant pH molecular dynamics simulations with coarse-grained modeling and yields new, atomic-level, insights into HdeA chaperone function that can be directly tested by experiment. “pH triggers” that significantly destabilize the dimer are each located near the N-terminus of a helix, suggesting that their neutralization at low pH destabilizes the helix macrodipole as a mechanism of monomer disordering. Moreover, we observe a non-monotonic change in the pH-dependent stability of HdeA, with maximal stability of the dimer near pH5. This affect is attributed to the protonation Glu37, which exhibits an anomalously high pK a value and is located within the hydrophobic dimer interface. Finally, the pH-dependent binding pathway of HdeA comprises a partially unfolded, dimeric intermediate that becomes increasingly stable relative to the native dimer at lower pH values and displays key structural features for chaperone–substrate interaction. We anticipate that the insights from our model will help inform ongoing NMR and biochemical investigations.
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    Categories: Journal Articles
  • A Hydrophobic Filter Confers the Cation Selectivity of Zygosaccharomyces rouxii Plasma-Membrane Na+/H+ Antiporter
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8

    Author(s): Olga Kinclova-Zimmermannova , Pierre Falson , Denis Cmunt , Hana Sychrova

    Na+/H+ antiporters may recognize all alkali-metal cations as substrates but may transport them selectively. Plasma-membrane Zygosaccharomyces rouxii Sod2-22 antiporter exports Na+ and Li+, but not K+. The molecular basis of this selectivity is unknown. We combined protein structure modeling, site-directed mutagenesis, phenotype analysis and cation efflux measurements to localize and characterize the cation selectivity region. A three-dimensional model of the ZrSod2-22 transmembrane domain was generated based on the X-ray structure of the Escherichia coli NhaA antiporter and primary sequence alignments with homologous yeast antiporters. The model suggested a close proximity of Thr141, Ala179 and Val375 from transmembrane segments 4, 5 and 11, respectively, forming a hydrophobic hole in the putative cation pathway's core. A series of mutagenesis experiments verified the model and showed that structural modifications of the hole resulted in altered cation selectivity and transport activity. The triple ZrSod2-22 mutant T141S-A179T-V375I gained K+ transport capacity. The point mutation A179T restricted the antiporter substrate specificity to Li+ and reduced its transport activity, while serine at this position preserved the native cation selectivity. The negative effect of the A179T mutation can be eliminated by introducing a second mutation, T141S or T141A, in the preceding transmembrane domain. Our experimental results confirm that the three residues found through modeling play a central role in the determination of cation selectivity and transport activity in Z. rouxii Na+/H+ antiporter and that the cation selectivity can be modulated by repositioning a single local methyl group.
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    Categories: Journal Articles
  • Allosteric Coupling via Distant Disorder-to-Order Transitions
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8

    Author(s): Christopher Eginton , William J. Cressman , Sharrol Bachas , Herschel Wade , Dorothy Beckett

    Intrinsic disorder provides a means of maximizing allosteric coupling in proteins. However, the mechanisms by which the disorder functions in allostery remain to be elucidated. Small ligand, bio-5′-AMP, binding and dimerization of the Escherichia coli biotin repressor are allosterically coupled. Folding of a disordered loop in the allosteric effector binding site is required to realize the full coupling free energy of −4.0±0.3kcal/mol observed in the wild-type protein. Alanine substitution of a glycine residue on the dimerization surface that does not directly contribute to the dimerization interface completely abolishes this coupling. In this work, the structure of this variant, solved by X-ray crystallography, reveals a monomeric corepressor-bound protein. In the structure loops, neither of which contains the alanine substitution, on both the dimerization and effector binding surfaces that are folded in the corepressor-bound wild-type protein are disordered. The structural data combined with functional measurements indicate that allosteric coupling between ligand binding and dimerization in BirA (E. coli biotin repressor/biotin protein ligase) is achieved via reciprocal communication of disorder-to-order transitions on two distant functional surfaces.
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    Categories: Journal Articles
  • FGFR3 Unliganded Dimer Stabilization by the Juxtamembrane Domain
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8

    Author(s): Sarvenaz Sarabipour , Kalina Hristova

    Receptor tyrosine kinases (RTKs) conduct biochemical signals upon dimerization in the membrane plane. While RTKs are generally known to be activated in response to ligand binding, many of these receptors are capable of forming unliganded dimers that are likely important intermediates in the signaling process. All 58 RTKs consist of an extracellular (EC) domain, a transmembrane (TM) domain, and an intracellular domain that includes a juxtamembrane (JM) sequence and a kinase domain. Here we investigate directly the effect of the JM domain on unliganded dimer stability of FGFR3, a receptor that is critically important for skeletal development. The data suggest that FGFR3 unliganded dimers are stabilized by receptor–receptor contacts that involve the JM domains. The contribution is significant, as it is similar in magnitude to the stabilizing contribution of a pathogenic mutation and the repulsive contribution of the EC domain. Furthermore, we show that the effects of the JM domain and a TM pathogenic mutation on unliganded FGFR3 dimer stability are additive. We observe that the JM-mediated dimer stabilization occurs when the JM domain is linked to FGFR3 TM domain and not simply anchored to the plasma membrane. These results point to a coordinated stabilization of the unliganded dimeric state of FGFR3 by its JM and TM domains via a mechanism that is distinctly different from the case of another well studied receptor, EGFR.
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    Categories: Journal Articles
  • Translation Elongation Factor EF-Tu Modulates Filament Formation of Actin-Like MreB Protein In Vitro
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8

    Author(s): Hervé Joël Defeu Soufo , Christian Reimold , Hannes Breddermann , Hans G. Mannherz , Peter L. Graumann

    EF-Tu has been shown to interact with actin-like protein MreB and to affect its localization in Escherichia coli and in Bacillus subtilis cells. We have purified YFP-MreB in an active form, which forms filaments on glass slides in vitro and was active in dynamic light-scattering assays, polymerizing in milliseconds after addition of magnesium. Purified EF-Tu enhanced the amount of MreB filaments, as seen by sedimentation assays, the speed of filament formation and the length of MreB filaments in vitro. EF-Tu had the strongest impact on MreB filaments in a 1:1 ratio, and EF-Tu co-sedimented with MreB filaments, revealing a stoichiometric interaction between both proteins. This was supported by cross-linking assays where 1:1 species were well detectable. When expressed in E. coli cells, B. subtilis MreB formed filaments and induced the formation of co-localizing B. subtilis EF-Tu structures, indicating that MreB can direct the positioning of EF-Tu structures in a heterologous cell system. Fluorescence recovery after photobleaching analysis showed that MreB filaments have a higher turnover in B. subtilis cells than in E. coli cells, indicating different filament kinetics in homologous or heterologous cell systems. The data show that MreB can direct the localization of EF-Tu in vivo, which in turn positively affects the formation and dynamics of MreB filaments. Thus, EF-Tu is a modulator of the activity of a bacterial actin-like protein.
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    Categories: Journal Articles
  • Phosphomimetic Mutation of the N-Terminal Lid of MDM2 Enhances the Polyubiquitination of p53 through Stimulation of E2-Ubiquitin Thioester Hydrolysis
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8

    Author(s): Jennifer A. Fraser , Erin G. Worrall , Yao Lin , Vivien Landre , Susanne Pettersson , Elizabeth Blackburn , Malcolm Walkinshaw , Petr Muller , Borek Vojtesek , Kathryn Ball , Ted R. Hupp

    Mouse double minute 2 (MDM2) has a phosphorylation site within a lid motif at Ser17 whose phosphomimetic mutation to Asp17 stimulates MDM2-mediated polyubiquitination of p53. MDM2 lid deletion, but not Asp17 mutation, induced a blue shift in the λmax of intrinsic fluorescence derived from residues in the central domain including Trp235, Trp303, Trp323, and Trp329. This indicates that the Asp17 mutation does not alter the conformation of MDM2 surrounding the tryptophan residues. In addition, Phe235 mutation enhanced MDM2 binding to p53 but did not stimulate its ubiquitination function, thus uncoupling increases in p53 binding from its E3 ubiquitin ligase function. However, the Asp17 mutation in MDM2 stimulated its discharge of the UBCH5a-ubiquitin thioester adduct (UBCH5a is a ubiquitin-conjugating enzyme E2D 1 UBC4/5 homolog yeast). This stimulation of ubiquitin discharge from E2 was independent of the p53 substrate. There are now four known effects of the Asp17 mutation on MDM2: (i) it alters the conformation of the isolated N-terminus as defined by NMR; (ii) it induces increased thermostability of the isolated N-terminal domain; (iii) it stimulates the allosteric interaction of MDM2 with the DNA-binding domain of p53; and (iv) it stimulates a novel protein–protein interaction with the E2-ubiquitin complex in the absence of substrate p53 that, in turn, increases hydrolysis of the E2-ubiquitin thioester bond. These data also suggest a new strategy to disrupt MDM2 function by targeting the E2-ubiquitin discharge reaction.
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    Categories: Journal Articles
  • Structure of an APC3–APC16 Complex: Insights into Assembly of the Anaphase-Promoting Complex/Cyclosome
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8

    Author(s): Masaya Yamaguchi , Shanshan Yu , Renping Qiao , Florian Weissmann , Darcie J. Miller , Ryan VanderLinden , Nicholas G. Brown , Jeremiah J. Frye , Jan-Michael Peters , Brenda A. Schulman

    The anaphase-promoting complex/cyclosome (APC/C) is a massive E3 ligase that controls mitosis by catalyzing ubiquitination of key cell cycle regulatory proteins. The APC/C assembly contains two subcomplexes: the “Platform” centers around a cullin-RING-like E3 ligase catalytic core; the “Arc Lamp” is a hub that mediates transient association with regulators and ubiquitination substrates. The Arc Lamp contains the small subunits APC16, CDC26, and APC13, and tetratricopeptide repeat (TPR) proteins (APC7, APC3, APC6, and APC8) that homodimerize and stack with quasi-2-fold symmetry. Within the APC/C complex, APC3 serves as center for regulation. APC3's TPR motifs recruit substrate-binding coactivators, CDC20 and CDH1, via their C-terminal conserved Ile-Arg (IR) tail sequences. Human APC3 also binds APC16 and APC7 and contains a >200-residue loop that is heavily phosphorylated during mitosis, although the basis for APC3 interactions and whether loop phosphorylation is required for ubiquitination are unclear. Here, we map the basis for human APC3 assembly with APC16 and APC7, report crystal structures of APC3Δloop alone and in complex with the C-terminal domain of APC16, and test roles of APC3's loop and IR tail binding surfaces in APC/C-catalyzed ubiquitination. The structures show how one APC16 binds asymmetrically to the symmetric APC3 dimer and, together with biochemistry and prior data, explain how APC16 recruits APC7 to APC3, show how APC3's C-terminal domain is rearranged in the full APC/C assembly, and visualize residues in the IR tail binding cleft important for coactivator-dependent ubiquitination. Overall, the results provide insights into assembly, regulation, and interactions of TPR proteins and the APC/C.
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    Categories: Journal Articles
  • Uncovering the Role of Sgf73 in Maintaining SAGA Deubiquitinating Module Structure and Activity
    [Apr 2015]

    Publication date: 24 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 8

    Author(s): Ming Yan , Cynthia Wolberger

    The SAGA (Spt–Ada–Gcn5 acetyltransferase) complex performs multiple functions in transcription activation including deubiquitinating histone H2B, which is mediated by a subcomplex called the deubiquitinating module (DUBm). The yeast DUBm comprises a catalytic subunit, Ubp8, and three additional subunits, Sgf11, Sus1 and Sgf73, all of which are required for DUBm activity. A portion of the non-globular Sgf73 subunit lies between the Ubp8 catalytic domain and the ZnF-UBP domain and has been proposed to contribute to deubiquitinating activity by maintaining the catalytic domain in an active conformation. We report structural and solution studies of the DUBm containing two different Sgf73 point mutations that disrupt deubiquitinating activity. We find that the Sgf73 mutations abrogate deubiquitinating activity by impacting the Ubp8 ubiquitin-binding fingers region and they have an unexpected effect on the overall folding and stability of the DUBm complex. Taken together, our data suggest a role for Sgf73 in maintaining both the organization and the ubiquitin-binding conformation of Ubp8, thereby contributing to overall DUBm activity.
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    Categories: Journal Articles
  • Atomic resolution structures of discrete stages on the reaction coordinate of the [Fe4S4] enzyme IspG (GcpE)
    [Apr 2015]

    Publication date: Available online 11 April 2015
    Source:Journal of Molecular Biology

    Author(s): Felix Quitterer , Annika Frank , Ke Wang , Guodong Rao , Bing O'Dowd , Jikun Li , Francisco Guerra , Safwat Abdel-Azeim , Adelbert Bacher , Jörg Eppinger , Eric Oldfield , Michael Groll

    IspG is the penultimate enzyme in non-mevalonate biosynthesis of the universal terpene building blocks isopentenyl diphosphate and dimethylallyl diphosphate. Its mechanism of action has been the subject of numerous studies but remained unresolved due to difficulties in identifying distinct reaction intermediates. Using a moderate reducing agent as well as an epoxide substrate analogue, we were now able to trap and crystallographically characterize various stages in the IspG catalyzed conversion of 2-C-methyl-D-erythritol-2,4-cyclo-diphosphate (MEcPP) to (E)-1-hydroxy-2-methylbut-2-enyl-4-diphosphate (HMBPP). In addition, the enzyme’s structure was determined in complex with several inhibitors. These results, combined with recent electron paramagnetic resonance data, allowed us to deduce a detailed and complete IspG catalytic mechanism which describes all stages from initial ring opening to formation of HMBPP via discrete radical and carbanion intermediates. The data presented in this article provide a guide for the design of selective drugs against many pro- and eukaryotic pathogens to which the non-mevalonate pathway is essential for survival and virulence.
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    Categories: Journal Articles
  • Sallimus and the dynamics of sarcomere assembly in Drosophila flight muscles
    [Apr 2015]

    Publication date: Available online 11 April 2015
    Source:Journal of Molecular Biology

    Author(s): Zacharias Orfanos , Kevin Leonard , Chris Elliott , Anja Katzemich , Belinda Bullard , John Sparrow

    The Drosophila indirect flight muscles (IFM) can be used as a model for the study of sarcomere assembly. Here we use a transgenic line with a GFP exon inserted into the Z-disc-proximal portion of Sallimus (Sls), also known as Drosophila titin, to observe sarcomere assembly during IFM development. Firstly we confirm that Sls-GFP can be used in the heterozygote state without an obvious phenotype in IFM and other muscles. We then use Sls-GFP in the IFM to show that sarcomeres grow individually and uniformly throughout the fibre, growing in length and diameter linearly. Finally, we show that limiting the amounts of Sls in the IFM using RNAi leads to sarcomeres with smaller Z-discs in their core, while the thick/thin filament lattice can form peripherally without a Z-disc. Thick filament preparations from those muscles show that although the Z-disc-containing core has thick filaments of a regular length, filaments from the peripheral lattice are longer and asymmetrical around the bare zone. Therefore the Z-disc and Sls are required for thick filament length specification, but not for the assembly of the thin/thick filament lattice.
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    Categories: Journal Articles
  • Editorial Board
    [Apr 2015]

    Publication date: 10 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 7









    Categories: Journal Articles
  • Contents List
    [Apr 2015]

    Publication date: 10 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 7









    Categories: Journal Articles
  • A First Line of Stress Defense: Small Heat Shock Proteins and Their Function in Protein Homeostasis
    [Apr 2015]

    Publication date: 10 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 7

    Author(s): Martin Haslbeck , Elizabeth Vierling

    Small heat shock proteins (sHsps) are virtually ubiquitous molecular chaperones that can prevent the irreversible aggregation of denaturing proteins. sHsps complex with a variety of non-native proteins in an ATP-independent manner and, in the context of the stress response, form a first line of defense against protein aggregation in order to maintain protein homeostasis. In vertebrates, they act to maintain the clarity of the eye lens, and in humans, sHsp mutations are linked to myopathies and neuropathies. Although found in all domains of life, sHsps are quite diverse and have evolved independently in metazoans, plants and fungi. sHsp monomers range in size from approximately 12 to 42kDa and are defined by a conserved β-sandwich α-crystallin domain, flanked by variable N- and C-terminal sequences. Most sHsps form large oligomeric ensembles with a broad distribution of different, sphere- or barrel-like oligomers, with the size and structure of the oligomers dictated by features of the N- and C-termini. The activity of sHsps is regulated by mechanisms that change the equilibrium distribution in tertiary features and/or quaternary structure of the sHsp ensembles. Cooperation and/or co-assembly between different sHsps in the same cellular compartment add an underexplored level of complexity to sHsp structure and function.
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    Categories: Journal Articles
  • Protein Quality Control under Oxidative Stress Conditions
    [Apr 2015]

    Publication date: 10 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 7

    Author(s): Jan-Ulrik Dahl , Michael J. Gray , Ursula Jakob

    Accumulation of reactive oxygen and chlorine species (RO/CS) is generally regarded to be a toxic and highly undesirable event, which serves as contributing factor in aging and many age-related diseases. However, it is also put to excellent use during host defense, when high levels of RO/CS are produced to kill invading microorganisms and regulate bacterial colonization. Biochemical and cell biological studies of how bacteria and other microorganisms deal with RO/CS have now provided important new insights into the physiological consequences of oxidative stress, the major targets that need protection, and the cellular strategies employed by organisms to mitigate the damage. This review examines the redox-regulated mechanisms by which cells maintain a functional proteome during oxidative stress. We will discuss the well-characterized redox-regulated chaperone Hsp33, and we will review recent discoveries demonstrating that oxidative stress-specific activation of chaperone function is a much more widespread phenomenon than previously anticipated. New members of this group include the cytosolic ATPase Get3 in yeast, the Escherichia coli protein RidA, and the mammalian protein α2-macroglobulin. We will conclude our review with recent evidence showing that inorganic polyphosphate (polyP), whose accumulation significantly increases bacterial oxidative stress resistance, works by a protein-like chaperone mechanism. Understanding the relationship between oxidative and proteotoxic stresses will improve our understanding of both host–microbe interactions and how mammalian cells combat the damaging side effects of uncontrolled RO/CS production, a hallmark of inflammation.
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    Categories: Journal Articles
  • Spatially Organized Aggregation of Misfolded Proteins as Cellular Stress Defense Strategy
    [Apr 2015]

    Publication date: 10 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 7

    Author(s): Stephanie B.M. Miller , Axel Mogk , Bernd Bukau

    An evolutionary conserved response of cells to proteotoxic stress is the organized sequestration of misfolded proteins into subcellular deposition sites. In Saccharomyces cerevisiae, three major sequestration sites for misfolded proteins exist, IPOD (insoluble protein deposit), INQ (intranuclear quality control compartment) [former JUNQ (juxtanuclear quality control compartment)] and CytoQ. IPOD is perivacuolar and predominantly sequesters amyloidogenic proteins. INQ and CytoQs are stress-induced deposits for misfolded proteins residing in the nucleus and the cytosol, respectively, and requiring cell-compartment-specific aggregases, nuclear Btn2 and cytosolic Hsp42 for formation. The organized aggregation of misfolded proteins is proposed to serve several purposes collectively increasing cellular fitness and survival under proteotoxic stress. These include (i) shielding of cellular processes from interference by toxic protein conformers, (ii) reducing the substrate burden for protein quality control systems upon immediate stress, (iii) orchestrating chaperone and protease functions for efficient repair or degradation of damaged proteins [this involves initial extraction of aggregated molecules via the Hsp70/Hsp104 bi-chaperone system followed by either refolding or proteasomal degradation or removal of entire aggregates by selective autophagy (aggrephagy) involving the adaptor protein Cue5] and (iv) enabling asymmetric retention of protein aggregates during cell division, thereby allowing for damage clearance in daughter cells. Regulated protein aggregation thus serves cytoprotective functions vital for the maintenance of cell integrity and survival even under adverse stress conditions and during aging.
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    Categories: Journal Articles
  • How Hsp70 Molecular Machines Interact with Their Substrates to Mediate Diverse Physiological Functions
    [Apr 2015]

    Publication date: 10 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 7

    Author(s): Eugenia M. Clerico , Joseph M. Tilitsky , Wenli Meng , Lila M. Gierasch

    Hsp70 molecular chaperones are implicated in a wide variety of cellular processes, including protein biogenesis, protection of the proteome from stress, recovery of proteins from aggregates, facilitation of protein translocation across membranes, and more specialized roles such as disassembly of particular protein complexes. It is a fascinating question to ask how the mechanism of these deceptively simple molecular machines is matched to their roles in these wide-ranging processes. The key is a combination of the nature of the recognition and binding of Hsp70 substrates and the impact of Hsp70 action on their substrates. In many cases, the binding, which relies on interaction with an extended, accessible short hydrophobic sequence, favors more unfolded states of client proteins. The ATP-mediated dissociation of the substrate thus releases it in a relatively less folded state for downstream folding, membrane translocation, or hand-off to another chaperone. There are cases, such as regulation of the heat shock response or disassembly of clathrin coats, however, where binding of a short hydrophobic sequence selects conformational states of clients to favor their productive participation in a subsequent step. This Perspective discusses current understanding of how Hsp70 molecular chaperones recognize and act on their substrates and the relationships between these fundamental processes and the functional roles played by these molecular machines.
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    Categories: Journal Articles
  • BiP and Its Nucleotide Exchange Factors Grp170 and Sil1: Mechanisms of Action and Biological Functions
    [Apr 2015]

    Publication date: 10 April 2015
    Source:Journal of Molecular Biology, Volume 427, Issue 7

    Author(s): Julia Behnke , Matthias J. Feige , Linda M. Hendershot

    BiP (immunoglobulin heavy-chain binding protein) is the endoplasmic reticulum (ER) orthologue of the Hsp70 family of molecular chaperones and is intricately involved in most functions of this organelle through its interactions with a variety of substrates and regulatory proteins. Like all Hsp70 family members, the ability of BiP to bind and release unfolded proteins is tightly regulated by a cycle of ATP binding, hydrolysis, and nucleotide exchange. As a characteristic of the Hsp70 family, multiple DnaJ-like co-factors can target substrates to BiP and stimulate its ATPase activity to stabilize the binding of BiP to substrates. However, only in the past decade have nucleotide exchange factors for BiP been identified, which has shed light not only on the mechanism of BiP-assisted folding in the ER but also on Hsp70 family members that reside throughout the cell. We will review the current understanding of the ATPase cycle of BiP in the unique environment of the ER and how it is regulated by the nucleotide exchange factors, Grp170 (glucose-regulated protein of 170 kDa) and Sil1, both of which perform unanticipated roles in various biological functions and disease states.
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    Categories: Journal Articles