The CH-domain of calponin does not determine the modes of calponin binding to F-actin

J Mol Biol. 2006 Jun 2;359(2):478-85. doi: 10.1016/j.jmb.2006.03.044. Epub 2006 Apr 3.


Many actin-binding proteins have been observed to have a modular architecture. One of the most abundant modules is the calponin-homology (CH) domain, found as tandem repeats in proteins that cross-link actin filaments (such as fimbrin, spectrin and alpha-actinin) or link the actin cytoskeleton to intermediate filaments (such as plectin). In proteins such as the eponymous calponin, IQGAP1, and Scp1, a single CH-domain exists, but there has been some controversy over whether this domain binds to actin filaments. A previous three-dimensional reconstruction of the calponin-F-actin complex has led to the conclusion that the visualized portion of calponin bound to actin belongs to its amino-terminal homology (CH) domain. We show, using a calponin fragment lacking the CH-domain, that this domain is not bound to F-actin, and cannot be positioning calponin on F-actin as hypothesized. Further, using classification methods, we show a multiplicity in cooperative modes of binding of calponin to F-actin, similar to what has been observed for other actin-binding proteins such as tropomyosin and cofilin. Our results suggest that the form and function of the structurally conserved CH-domain found in many other actin-binding proteins have diverged. This has broad implications for inferring function from the presence of structurally conserved domains.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Actins / metabolism*
  • Actins / ultrastructure
  • Animals
  • Calcium-Binding Proteins / chemistry*
  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / metabolism*
  • Calcium-Binding Proteins / ultrastructure
  • Crystallography, X-Ray
  • Image Processing, Computer-Assisted
  • Microfilament Proteins / chemistry*
  • Microfilament Proteins / genetics
  • Microfilament Proteins / metabolism*
  • Microfilament Proteins / ultrastructure
  • Models, Molecular
  • Peptide Fragments / chemistry
  • Peptide Fragments / genetics
  • Peptide Fragments / metabolism
  • Protein Binding
  • Protein Conformation*


  • Actins
  • Calcium-Binding Proteins
  • Microfilament Proteins
  • Peptide Fragments
  • calponin