Generation of functional β-actinin (CapZ) in an E. coli expression system

β-actinin (CapZ) is a heterodimeric actin-binding protein which caps the barbed end of actin filaments and nucleates actin-polymerization in a Ca2+-independent manner. In myofibrils it is localized in the Z-lines. As judged by these properties of β-actinin, it is conceivable that β-actinin is involved in the regulation of actin assembly, especially in the formation of I-Z-I complex during myofibrillogenesis. In this study, we devised a system to produce functional β-actinin in E. Coli.The cDNAs of βI′ and βII subunits of β-actinin were obtained by RT-PCR methods using the published sequence as references, and subcloned in a pET vector. When the proteins were produced with the cDNA of either βI′ or βII in E. coli, the proteins were insoluble and non-functional. However, when the cDNAs encoding the two subunits were cloned into a single vector and␣both proteins were expressed simultaneously, the proteins became soluble and purified as a functional heterodimer. The␣activity of the purified proteins was not distinguishable from that of β-actinin purified from skeletal muscle.