Calponin interaction with alpha-actinin-actin: evidence for a structural role for calponin.

Abstract

The purpose of this study was to address the paradox of calponin localization with a-actinin and filamin, two proteins with tandem calponin homology (CH) domains, by determining the effect of these proteins on the binding of calponin to actin. The results show that actin can accommodate near-saturating concentrations of either calponin and a-actinin or calponin and filamin with little change or no change in ligand affinity. Little direct interaction occurred between a-actinin and calponin in the absence of actin, so this effect is not likely to explain the co-distribution of these proteins. Calponin, like a-actinin, induced elastic gel formation when added to actin. When a-actinin was added to newly formed calponin/actin gels, no change was seen in the mechanical properties of the gel compared to calponin and actin alone. However, when calponin was added to newly formed a-actinin/actin gels, the resulting gel was much stronger than the gels formed by either ligand alone. Furthermore, gels formed by the addition of calponin to a-actinin/actin exhibited a phenomenon known as strain hardening, a characteristic of mechanically resilient gels. These results add weight to the concept that one of the functions of calponin is to stabilize the actin cytoskeleton. Originally published Biophysical Journal, Vol. 77, No. 6, Dec 1999