The carboxyl‐terminal region of ahnak provides a link between cardiac L‐type Ca2+channels and the actinbased cytoskeleton

Abstract

Ahnak is a ubiquitously expressed giant protein of 5643 amino acids implicated in cell differentiation and signal transduction. In a recent study, we demonstrated the association of ahnak with the regulatory β2 subunit of the cardiac L-type Ca²⁺ channel. Here we identify the most carboxyl-terminal ahnak region (aa 5262–5643) to interact with recombinant β2a as well as with β2 and β1a isoforms of native muscle Ca²⁺ channels using a panel of GST fusion proteins. Equilibrium sedimentation analysis revealed K_d values of 55 ± 11 nM and 328 ± 24 nM for carboxyl-terminal (aa 195–606) and amino-terminal (aa 1–200) truncates of the β2a subunit, respectively. The same carboxyl-terminal ahnak region (aa 5262–5643) bound to G-actin and cosedimented with F-actin. Confocal microscopy of human left ventricular tissue localized the carboxyl-terminal ahnak portion to the sarcolemma including the T-tubular system and the intercalated disks of cardiomyocytes. These results suggest that ahnak provides a structural basis for the subsarcolemmal cytoarchitecture and confers the regulatory role of the actin-based cytoskeleton to the L-type Ca²⁺ channel.—Hohaus, A., Person, V., Behlke, J., Schaper, J., Morano, I., Haase, H. The carboxyl-terminal region of ahnak provides a link between cardiac L-type Ca²⁺ channels and the actin-based cytoskeleton.