Research

CapZ-lipid membrane interactions: a computer analysis

James Smith , Gerold Diez , Anna H Klemm , Vitali Schewkunow and Wolfgang H Goldmann

Friedrich-Alexander-University of Erlangen-Nuremberg Center for Medical Physics and Technology, Biophysics Group Henkestrasse 91, 91052 Erlangen, Germany

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Theoretical Biology and Medical Modelling 2006, 3:30doi:10.1186/1742-4682-3-30

Published:	16 August 2006

Abstract

Background

CapZ is a calcium-insensitive and lipid-dependent actin filament capping protein, the main function of which is to regulate the assembly of the actin cytoskeleton. CapZ is associated with membranes in cells and it is generally assumed that this interaction is mediated by polyphosphoinositides (PPI) particularly PIP₂, which has been characterized in vitro.

Results

We propose that non-PPI lipids also bind CapZ. Data from computer-aided sequence and structure analyses further suggest that CapZ could become partially buried in the lipid bilayer probably under mildly acidic conditions, in a manner that is not only dependent on the presence of PPIs. We show that lipid binding could involve a number of sites that are spread throughout the CapZ molecule i.e., alpha- and beta-subunits. However, a beta-subunit segment between residues 134–151 is most likely to be involved in interacting with and inserting into lipid membrane due to a slighly higher ratio of positively to negatively charged residues and also due to the presence of a small hydrophobic helix.

Conclusion

CapZ may therefore play an essential role in providing a stable membrane anchor for actin filaments.