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  • The EMBO Journal (2006) 25, 4458 - 4467
  • doi:10.1038/sj.emboj.7601323

Published online: 14 September 2006

A CapG gain-of-function mutant reveals critical structural and functional determinants for actin filament severing

Y Zhang1,a, Sergey M Vorobiev2,a, Bruce G Gibson1, Binghua Hao1, Gurjit S Sidhu1, Vishnu S Mishra1, Elena G Yarmola1, Michael R Bubb1, Steven C Almo3 and Frederick S Southwick1

  1. Department of Medicine, University of Florida, Gainesville, FL, USA
  2. Department of Biology, Columbia University, New York, NY, USA
  3. Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY, USA

Correspondence to:

Frederick S Southwick, Department of Medicine/Infectious Diseases, University of Florida, College of Medicine, Box 100277, 1600 Archer Road, Gainesville, FL 32610, USA. Tel.: +1 352 392 4058; Fax: +1 352 392 6481; E-mail: southfs@medicine.ufl.edu

Steven C Almo, Department of Biochemistry, Albert Einstein College of Medicine, Ullmann Building, Room 411, 1300 Morris Park Avenue, Bronx, NY 10461, USA. Tel.: +1 718 430 2746; Fax: +1 718 430 8565; E-mail: almo@aecom.yu.edu

aThese authors contributed equally to this work

Received 26 April 2006; Accepted 2 August 2006

CapG is the only member of the gelsolin family unable to sever actin filaments. Changing amino acids 84–91 (severing domain) and 124–137 (WH2-containing segment) simultaneously to the sequences of gelsolin results in a mutant, CapG-sev, capable of severing actin filaments. The gain of severing function does not alter actin filament capping, but is accompanied by a higher affinity for monomeric actin, and the capacity to bind and sequester two actin monomers. Analysis of CapG-sev crystal structure suggests a more loosely folded inactive conformation than gelsolin, with a shorter S1–S2 latch. Calcium binding to S1 opens this latch and S1 becomes separated from a closely interfaced S2–S3 complex by an extended arm consisting of amino acids 118–137. Modeling with F-actin predicts that the length of this WH2-containing arm is critical for severing function, and the addition of a single amino acid (alanine or histidine) eliminates CapG-sev severing activity, confirming this prediction. We conclude that efficient severing utilizes two actin monomer-binding sites, and that the length of the WH2-containing segment is a critical functional determinant for severing.

  • Keywords:

    • actin-regulatory proteins,
    • CapG,
    • gelsolin,
    • severing,
    • WH2