Bingdong Sha - US grants

DESCRIPTION (provided by applicant): The long-term goat of this proposal is to carry out X-ray crystallographic studies on Hsp40 to uncover the basic mechanisms by which Hsp40 interacts with non-native polypeptides and cooperates with Hsp70 to perform the molecular chaperone activity. We have proposed an "anchoring and docking" model to illustrate the mechanisms for Hsp40 to interact with HspT0. To support this hypothesis, we intend to determine the crystal structure of the yeast type II Hsp40 Sis1 complexed with yeast Hsp70 Ssa1. We have constituted and crystallized the protein complex of Sis1 peptide-binding fragment and the Ssal C-terminal domain. Once solved, the complex crystal structure of Sis1 and Ssa1 will inform us how Hsp40 interacts with Hsp70 to carry out the non-native polypeptide delivery and assists Hsp in protein folding. The crystal structure of yeast type I Hsp40 Ydjl, complexed with the peptide substrate GWLYEIS, indicates that the pocket on the molecular surface of Ydjl may play important roles in peptide substrate binding. This pocket may exhibit significant plasticity to accommodate various sizes of hydrophobic side chains. We propose to determine the crystal structures of Ydjl peptide-binding fragment, complexed with peptide substrates GWWYEIS, and GWAYEIS. The crystal structures of Ydj1 and various peptide substrates may provide the structural basis of how Hsp40 adjusts itself to accommodate different peptide substrates. To reveal the mechanism by which Hsp40 primes the non-native polypeptide for the subsequent Hsp70 binding, we have designed a non-native polypeptide, Y1, by connecting two Hsp40 Ydj1 peptide substrates GWLYEIS with a flexible linker. The recombinant polypeptide Y1 showed a reasonable binding affinity to Hsp40 Ydjl. We intend to crystallize and determine the structure of the Ydjl complexed with the "non-native polypeptide", Y1, to illustrate how Hsp40 may affect the conformation of the non-native polypeptide. Finally, we will conduct structure-based mutagenesis studies to test our proposed models for the mechanisms of Hsp40 chaperone actions.

[unreadable] DESCRIPTION (provided by applicant): The goals of this proposal are to carry out structural studies on Hspl 00 to uncover the mechanisms by which it functions as a molecular chaperone. E. coli Hspl 00 ClpB was recently identified to act as a molecular chaperone by disaggregating non-native polypeptides. To investigate the mechanisms for HsplOO CIpB to disaggregate non-native polypeptides, we propose to determine ClpB N-terminal domain structure. The CIpB N-terminal domain has been shown to interact directly with non-native polypeptides and play essential roles in CIpB chaperone functions. We have crystallized the N-terminal domain of ClpB and the crystals diffracted X-ray to I .95A. In the structure of CIpB N-terminal domain, we may identify a peptide-binding groove. Therefore, we could predict the minimal length of peptides bound by Hspl 00 CIpB. The high affinity peptide substrates of CIpB will be identified by genetic and biophysical approaches. We will crystallize the complex of CIpB N-terminal domain with its peptide substrate. The crystal structure of the complex will provide fundamental insights on how HsplOO CIpB recognizes and binds the non-native polypeptides. To reveal the mechanisms for CIpB to carry out its ATPase activities, we propose to determine the crystal structure of CIpB nucleotide-binding domain 2 with the C-terminal fragment (D2C). CIpB contains two nucleotide-binding domains NBDI and NBD2. We have solved the crystal structure of CIpB NBDI and have crystallized CIpB D2C complexed with ATP or ADP. To test the models for the mechanisms for HsplOO CIpB chaperone functions, we will construct two sets of structure-based CIpB mutants. One is to mutate residues within ClpB N-terminal domain that are critically involved in binding peptides. These mutants will be tested for loss of functions by peptide binding assays and protein folding assays. The other set of mutants is to support the proposed "See-Saw" model for CIpB ATPase activity. We will mutate residues to disable the conformational changes of the CIpB C-terminal fragment. The mutants will be tested for functions by nucleotide binding assays, ATPase activity assays and protein folding assays. Collectively, this proposal covers a comprehensive study that reveals the mechanisms by which ClpB interacts with non-native polypeptides and perform ATP hydrolysis to function as a molecular chaperone.

structural biology; molecular chaperones; protein structure; biomedical resource;

DESCRIPTION (provided by applicant): Protein translocations across mitochondria membranes play critical roles in mitochondria biogenesis. The protein transports from the cell cytosol to the mitochondria are carried out by the translocase of the outer membrane (TOM) complex and the translocase of the inner membrane (TIM) complex. (1) In the TOM complex, Tom70 functions as the receptor for mitochondria precursors with internal targeting signals. In our Tom70 crystal structure, the C-terminal domain of Tom70 forms a large pocket which may represent the binding site for mitochondrial precursor and the N-terminal domain of Tom70 may function to gate the pocket. Interestingly, the gating of the precursor-binding pocket of Tom70 is regulated by Hsp70/Hsp90 binding. The crystal structure of Tom70-Hsp70/Hsp90 complex indicates that the C-terminal EEVD motifs of Hsp70/Hsp90 can maintain Tom70 in the open conformation for receiving mitochondrial precursor. To fully understand the mechanism how Tom70 interacts with its peptide substrate under the regulation of Hsp70/Hsp90, we have identified a peptide substrate P70-8 for Tom70-Hsp70 complex by phage display library screening. The crystal structure of Tom70-Hsp70 EEVD motif-peptide substrate complex will illustrate the mechanism how Tom70 functions as a receptor for the molecular chaperone-bound mitochondrial precursor in the TOM translocon. Structure-based mutagenesis studies will be performed to confirm our hypothesis. (2) In the TIM23 translocon, Tim50 functions as a receptor to guide the precursor with the N-terminal presequence to the inner membrane protein channel Tim23 for translocation. Tim50IMS may interact with the presequence. Tim50IMS can also interact with Tim23IMS to deliver the precursors to the transmembrane channel formed by the C-terminal domain of Tim23. Our crystal structure of Tim50IMS indicated a protruding ¿-hairpin may represent the binding site for Tim23. Close to this ¿-hairpin, Tim50 contains a large groove that may represent the binding site for the presequence. We intend to determine the crystal structures of Tim50IMS-presequence complex, Tim50IMS- Tim23IMS complex and Tim50IMS-Tim23IMS-presequence complex. (3) Tim23 represents the major component in TIM23 translocon and it forms the essential transmembrane channel in the mitochondrial inner membrane. To reveal the mechanism how this important membrane protein transports mitochondrial precursors, we propose to determine the crystal structure of Tim23. Tim23 has been known to be difficult to express using a number of systems. In preliminary data, we have developed a crystallization chaperone for yeast Tim23IMS using phage display library screening. We have successfully expressed Tim23 complexed with the crystallization chaperone using the self-cleaving 2A peptide in Pichia system. The recombinant Tim23 is functional as shown by electrophysiological analysis using planar lipid bilayer system.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Protein translocations across mitochondria membranes play critical roles in mitochondria biogenesis. The protein transports from the cell cytosol to the mitochondria matrix are carried out by the translocase of the outer membrane (TOM) complex and the translocase of the inner membrane (TIM) complex. In the TIM23 translocon, Tim50 functions as a receptor to guide the precursor with the N-terminal mitochondrion targeting sequence to the inner membrane protein channel for translocation. Recently we have crystallized yeast Tim50. The crystallographic studies on yeast TIM23 translocon will uncover the basic mechanisms how the translocons facilitate the protein translocations across the mitochondria outer and inner membranes.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Tail-anchored (TA) proteins represent a unique family of transmembrane proteins which contain a single transmembrane helix (about 25 residues) at the C-terminus. The mechanisms how the TA proteins insert the TMD into membranes are distinct from the well-studied co-translational insertion pathway, which is mediated by the cytosolic signal recognition particle (SRP). The post-translational insertion of the TA proteins into ER membrane requires the Golgi ER trafficking (GET) complex which contains Get1, Get2 and Get3. Get3 is an ATPase and can recognize and bind the C- terminal transmembrane domain (TMD) of the TA proteins. It is not well understood how GET complex accomplish the membrane insertion of the TA protein. Recently we have determined the yeast Get3 crystal structure in the open conformation. The structure suggested that Get3 may adopt an open conformation in nucleotide-free state and a closed conformation in ATP-bound state. The conformational changes to switch the Get3 between the open and closed conformations may facilitate the membrane insertions for TA proteins. Get3 may share a similar mechanism as the ABC transporters to transfer bound ligands. Now we are requesting beam time to determine Get3 crystal structure in the closed conformation to confirm our hypothesis.

Disturbance in the folding capacity of endoplasmic reticulum (ER) prompts a cellular condition known as ER stress. ER stress is induced in neurodegenerative diseases including Alzheimer?s disease (AD). PERK is one of the major ER stress sensor proteins which can be activated by misfolded protein in ER luminal domain to initiate the ER stress. Accumulating evidences have demonstrated that the PERK activation is closely associated with the pathogenesis of AD. PERK activation can lead to overexpression of BACE1, the deposition of amyloid ? (A?) plaques and the phosphorylation of tau protein. Prolonged PERK activation may also cause the neuronal loss by apoptosis. Solid data from AD animal models have shown that depletion or inhibition of PERK may exhibit substantial neuroprotection and reduce the amount of AD-related plaques in the AD brains. However, the existing PERK inhibitors are ATP-analogues and represent high toxicity and low specificity in vivo. Our data support the hypothesis that misfolded proteins can directly interact with PERK to activate the PERK signaling pathway. We propose to identify novel inhibitors of PERK that can block the interactions between PERK luminal domain and the misfolded protein by high throughput screening. These small molecular inhibitors may represent novel treatments for AD by attenuating the ER stress signals. We have determined the complex crystal structure of PERK luminal domain and its peptide substrate, which allows us to optimize the identified inhibitors by use of structure-based drug design.

Recent explosion in genomic medicine studies has led to identification of an increasing number of genomic variations from patients with congenital defects. However, detailed analyses about how the variants affect developmental processes are scarce, resulting in a growing class of variants classified as variants of uncertain significance (VUS). Understanding functional consequences of VUS will help patients, their families, and their doctors to learn genetic underpinnings of their conditions, enable clinicians to provide personalized medical care and treatment, and expand our knowledge on biology and mechanistic operations of the molecules involved in disease processes. In this proposal, we plan to employ multidisciplinary approaches to investigate the YWHAZ variants associated with congenital syndromes. Our preliminary studies on one variant identified from a patient with RASopathy revealed that the variant activated the RAF-ERK pathway more efficiently than wild type YWHAZ in a vertebrate animal model, the African clawed frog Xenopus. The results show for the first time that YWHAZ variant may contribute to etiology of RASopathies. Several other YWHAZ variants also associate with human disorders, but functional significance of the variants has not been examined. Our proposed research will leverage the advantages of the Xenopus model, the power of biochemical and structural studies, and the strength of the mouse genetic system for detailed characterization of the YWHAZ variants. We will investigate whether and how YWHAZ variants have altered activities (aim 1), how sequence variations affect protein structure and interaction (aim 2), and how the variants induce pathology in the mouse models (aim 3). The novel combination of our investigation teams with expertise in distinct research disciplines promises generation of profound insight into disease- associated YWHAZ gene function and mechanisms.