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ABSTRACT: The interactions of huntingtin (Htt) with the SH3 domain- or WW domain-containing proteins have been implicated in the pathogenesis of Huntington's disease (HD). We report the specific interactions of Htt proline-rich region (PRR) with the SH3GL3-SH3 domain and HYPA-WW1-2 domain pair by NMR. The results show that Htt PRR binds with the SH3 domain through nearly its entire chain, and that the binding region on the domain includes the canonical PxxP-binding site and the specificity pocket. The C terminus of PRR orients to the specificity pocket, whereas the N terminus orients to the PxxP-binding site. Htt PRR can also specifically bind to WW1-2; the N-terminal portion preferentially binds to WW1, while the C-terminal portion binds to WW2. This study provides structural insights into the specific interactions between Htt PRR and its binding partners as well as the alteration of these interactions that involve PRR, which may have implications for the understanding of HD.
Structure 01/2007; 14(12):1755-65. · 6.35 Impact Factor
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ABSTRACT: CcmG, also designated DsbE, functions as a periplasmic protein thiol:disulfide oxidoreductase and is required for cytochrome c maturation. Here we report the crystal structures of Escherichia coli CcmG and its two mutants, P144A and the N-terminal fifty seven-residue deletion mutant, and two additional deletion mutants were studied by circular dichroism. Structural comparison of E. coli CcmG with its deletion mutants reveals that the N-terminal beta-sheet is essential for maintaining the folding topology and consequently maintaining the active-site structure of CcmG. Pro144 and Glu145 are key residues of the fingerprint region of CcmG. Pro144 is in cis-configuration, and it makes van der Waals interactions with the active-site disulfide Cys80-Cys83 and forms a C--H...O hydrogen bond with Thr82, helping stabilize the active-site structure. Glu145 forms a salt-bridge and hydrogen-bond network with other residues of the fingerprint region and with Arg158, further stabilizing the active-site structure. The cis-configuration of Pro144 makes the backbone nitrogen and oxygen of Ala143 exposed to solvent, favorable for interacting with binding partners. The key role of cis-Pro144 is verified by the P144A mutant, which contains trans-Ala144 and displays redox property changes. Structural comparison of E. coli CcmG with the recently reported structure of CcmG in complex with the N-terminal domain of DsbD reveals that Tyr141 undergoes conformational changes upon binding DsbD. A cis-proline located at the N-terminus of the first beta-strand of the betabetaalpha motif of the thioredoxin-like domain is a conserved structural feature of the thioredoxin superfamily.
Proteins Structure Function and Bioinformatics 01/2007; 65(4):1021-31. · 3.39 Impact Factor
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ABSTRACT: Ubiquitin is an important cellular signal that targets proteins for degradation or regulates their functions. The previously identified BMSC-UbP protein derived from bone marrow stromal cells contains a ubiquitin-associated (UBA) domain at the C terminus that has been implicated in linking cellular processes and the ubiquitin system. Here, we report the solution NMR structure of the UBA domain of human BMSC-UbP protein and its complex with ubiquitin. The structure determination was facilitated by using a solubility-enhancement tag (SET) GB1, immunoglobulin G binding domain 1 of Streptococcal protein G. The results show that BMSC-UbP UBA domain is primarily comprised of three alpha-helices with a hydrophobic patch defined by residues within the C terminus of helix-1, loop-1, and helix-3. The M-G-I motif is similar to the M/L-G-F/Y motifs conserved in most UBA domains. Chemical shift perturbation study revealed that the UBA domain binds with the conserved five-stranded beta-sheet of ubiquitin via hydrophobic interactions with the dissociation constant (KD) of approximately 17 microM. The structural model of BMSC-UbP UBA domain complexed with ubiquitin was constructed by chemical shift mapping combined with the program HADDOCK, which is in agreement with the result from mutagenesis studies. In the complex structure, three residues (Met76, Ile78, and Leu99) of BMSC-UbP UBA form a trident anchoring the domain to the hydrophobic concave surface of ubiquitin defined by residues Leu8, Ile44, His68, and Val70. This complex structure may provide clues for BMSC-UbP functions and structural insights into the UBA domains of other ubiquitin-associated proteins that share high sequence homology with BMSC-UbP UBA domain.
Protein Science 07/2006; 15(6):1248-59. · 2.80 Impact Factor
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ABSTRACT: It is often essential to focus the study on the small-size domains of large proteins in eukaryotic cells in the post-genomic era, but the low expression level, insolubility, and instability of the domains have been continuing to hinder the massive purification of domain peptides for structural and biological investigation. In this work, a highly efficient expression and purification system based on a small-size fusion partner GB1 and histidine tag was utilized to solve these problems. Two vectors, namely pGBTNH and pGBH, were constructed to improve expression and facilitate purification. The linker and thrombin cleavage site have been optimized for minimal degradation during purification process. This system has been tested for eight domain peptides varying in size, linker, hydrophobicity, and predicted secondary structure. The results indicate that this system is achievable to produce these domain peptides with high solubility and stability for further biochemical characterization. Moreover, the fusion protein without the linker and thrombin cleavage site is also suitable for spectroscopic studies especially for NMR structural elucidation, if the target peptide is prone to precipitation or easily degraded during purification. This system will be beneficial to the research field of structure and function of small domain and peptide fragment.
Protein Expression and Purification 07/2006; 47(2):599-606. · 1.59 Impact Factor
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ABSTRACT: The previously identified dendritic cell-derived ubiquitin-like protein (DC-UbP) was implicated in cellular differentiation and apoptosis. Sequence alignment suggested that it contains a ubiquitin-like (UbL) domain in the C terminus. Here, we present the solution NMR structure and backbone dynamics of the UbL domain of DC-UbP. The overall structure of the domain is very similar to that of Ub despite low similarity (<30%) in amino-acid sequence. One distinct feature of the domain structure is its highly positively charged surface that is different from the corresponding surfaces of the well-known UbL modifiers, Ub, NEDD8, and SUMO-1. The key amino-acid residues responsible for guiding polyubiquitinated proteins to proteasome degradation in Ub are not conserved in the UbL domain. This implies that the UbL domain of DC-UbP may have its own specific interaction partners with other yet unknown cellular functions related to the Ub pathway.
Protein Science 09/2005; 14(8):2044-50. · 2.80 Impact Factor
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ABSTRACT: HSPC144 is a newly identified gene in human CD34(+) hematopoietic stem/progenitor cells. In this work, we have expressed and purified the 225-residue protein from Escherichia coli BL21 (DE3) and identified a stable fragment HSPC144-P (residues 44-225) by limited proteolysis method. The HSPC144-P fragment exhibits high stability with a little increase of secondary structure percentage as compared with the full-length protein. We anticipated that the N-terminally truncated protein possesses a more compact structure. By sequence analysis, the proteolytic fragment shares a great similarity with DUF589 domain, a previously identified domain with unknown function. This novel domain is highly conserved in Thy28 proteins and is worthy of structural and functional studies. We have subcloned this homologous domain from HSPC144 protein and purified to homogeneity for structure analysis. The (15)N and (15)N/(13)C-labeled DUF589 domain samples have been prepared successfully and determination of the NMR structure is in progress.
Protein Expression and Purification 08/2005; 42(1):146-52. · 1.59 Impact Factor
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ABSTRACT: CcmG/DsbE is a typical thiol/disulfide oxidoreductase, exhibiting a specific reducing activity in a highly oxidizing environment, and is involved in electron transfer during the maturation of c-type cytochromes. Escherichia coli CcmG/DsbE (residues 19-185) has been crystallized using the hanging-drop vapour-diffusion technique. The crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 35.48, b = 48.52, c = 84.78 A. X-ray data have been collected to 1.9 A resolution.
Acta Crystallographica Section D Biological Crystallography 10/2003; 59(Pt 9):1674-5. · 12.62 Impact Factor
