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Biophys. J. BioFAST: First Published October 8, 2004. doi:10.1529/biophysj.104.051128
© 2004 by the Biophysical Society.

A more recent version of this article appeared on January 1, 2005.
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MUSCLE AND CONTRACTILITY

Structure and Tropomyosin Binding Properties of the N-terminal Capping Domain of Tropomodulin 1

Norma J. Greenfield 1*, Alla S. Kostyukova 1 and Sarah E. Hitchcock-DeGregori 1

1 UMDNJ-Robert Wood Johnson Medical School

* To whom correspondence should be addressed. E-mail: greenfie{at}rwja.umdnj.edu.

Submitted on August 6, 2004
Revised on August 25, 2004
Accepted on 27 September 2004


  Abstract
ABSTRACT Two families of actin regulatory proteins are the tropomodulins and tropomyosins. Tropomodulin binds to tropomyosin (TM) and to the pointed end of actin filaments and "caps" the pointed end (i.e. inhibits its polymerization and depolymerization). Tropomodulin 1 has two distinct actin-capping regions: a folded C-terminal domain (residues 160-359), which does not bind to TM, and a conserved, N terminal region, within residues 1-92, which binds TM and requires TM for capping activity. NMR and CD were used to determine the structure of a peptide containing residues 1-92 of tropomodulin, Tmod11-92, and to define its TM binding site. Tmod11-92 is mainly disordered with only one helical region, residues 24-35. This helix forms part of the TM binding domain, residues 1-35, which become more ordered upon binding a peptide containing the N terminus of an {alpha}-TM. Mutation of L27 to E or G in the Tmod helix inhibits TM binding. Residues 49-92, are required for capping but do not bind TM. Of these, residues 67-75 have the sequence of an amphipathic helix, but are not helical. Residues 55-62 and 76-92 display negative 1H-15N heteronuclear NOEs showing they are flexible. The conformational dynamics of these residues may be important for actin capping activity

Key Words: NMR, actin, binding, circular dichroism, tropomodulin, tropomyosin




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Copyright © 2004 by the Biophysical Society.