Thymosin beta(4) binds actin in an extended conformation and contacts both the barbed and pointed ends

被引:91
作者
Safer, D
Sosnick, TR
Elzinga, M
机构
[1] UNIV PENN,JOHNSON RES FDN,DEPT BIOCHEM & BIOPHYS,PHILADELPHIA,PA 19104
[2] NEW YORK STATE INST BASIC RES DEV DISABIL,DEPT PHARMACOL,STATEN ISL,NY 10314
关键词
D O I
10.1021/bi970185v
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The beta-thymosins are a family of highly polar peptides which serve in vivo to maintain a reservoir of unpolymerized actin monomers. In vitro, beta-thymosins form 1:1 complexes with actin monomers and inhibit both polymerization and exchange of the bound nucleotide. Circular dichroism data indicate that free thymosin beta(4) is predominantly unstructured, containing at most six residues of alpha-helix, and that up to six additional residues may adopt an alpha-helical conformation upon binding actin. NMR data indicate that many parts of thymosin beta(4) are not in tight contact with actin. Contacts between specific residues in actin and thymosin beta(4) were identified by zero-length cross-linking followed by isolation and sequencing of cross-linked peptides. After carbodiimide-mediated cross-linking, Lys-3 of thymosin beta(4) was cross-linked to Glu-167 of actin, and Lys-18 of thymosin beta(4) was cross-linked to one of the the N-terminal acidic residues of actin (Asp-1- Glu-4); the cross-linked actin residues lie within subdomains 3 and 1, respectively. These two contacts flank the ex-helical region of thymosin beta 4 and place it on the barbed end; thymosin beta(4) can thus block actin polymerization sterically. After transglutaminase-mediated cross-linking, Lys-38 of thymosin beta(4) was cross-linked to Gln-41 of actin, placing the C-terminal region of thymosin beta 4 in contact with subdomain 2 on the pointed end; thymosin beta 4 may sterically block actin polymerization at the pointed end as well as the barbed end of the monomer. The distance between the pointed-end and barbed-end contacts requires that the C-terminal half of thymosin beta(4) be in a predominantly extended conformation.
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页码:5806 / 5816
页数:11
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