Structure of a Longitudinal Actin Dimer Assembled by Tandem W Domains: Implications for Actin Filament Nucleation

JOURNAL OF MOLECULAR BIOLOGY

卷:403

Article

Rebowski, Grzegorz¹  Namgoong, Suk¹  Boczkowska, Malgorzata¹  Leavis, Paul C.²  Navaza, Jorge³  Dominguez, Roberto¹ 

[1] Univ Penn, Sch Med, Dept Physiol, Philadelphia, PA 19104 USA

[2] Boston Biomed Res Inst, Watertown, MA 02472 USA

[3] Inst Biol Struct, F-38027 Grenoble, France

关键词: actin nucleation;    W domain;    nucleation-promoting factors;    T beta 4;    actin monomer sequestration;   

DOI  :  10.1016/j.jmb.2010.08.040

来源: Elsevier

【 摘 要 】

Actin filament nucleators initiate polymerization in cells in a regulated manner. A common architecture among these molecules consists of tandem WASP homology 2 domains (W domains) that recruit three to four actin subunits to form a polymerization nucleus. We describe a low-resolution crystal structure of an actin dimer assembled by tandem W domains, where the first W domain is cross-linked to Cys374 of the actin subunit bound to it, whereas the last W domain is followed by the C-terminal pointed end-capping helix of thymosin beta 4. While the arrangement of actin subunits in the dimer resembles that of a long-pitch helix of the actin filament, important differences are observed. These differences result from steric hindrance of the W domain with intersubunit contacts in the actin filament. We also determined the structure of the first W domain of Vibrio parahaemolyticus VopL cross-linked to actin Cys374 and show it to be nearly identical with non-cross-linked W-Actin structures. This result validates the use of cross-linking as a tool for the study of actin nucleation complexes, whose natural tendency to polymerize interferes with most structural methods. Combined with a biochemical analysis of nucleation, the structures may explain why nucleators based on tandem W domains with short inter-W linkers have relatively weak activity, cannot stay bound to filaments after nucleation, and are unlikely to influence filament elongation. The findings may also explain why nucleation-promoting factors of the Arp2/3 complex, which are related to tandem-W-domain nucleators, are ejected from branch junctions after nucleation. We finally show that the simple addition of the C-terminal pointed end-capping helix of thymosin beta 4 to tandem W domains can change their activity from actin filament nucleation to monomer sequestration. (C) 2010 Elsevier Ltd. All rights reserved

【 授权许可】

Free