Sarcomeric and nonmuscle ?-actinin isoforms exhibit differential dynamics at skeletal muscle Z-lines.

ABSTRACT: The ?-actinin proteins are a highly conserved family of actin crosslinkers that mediate interactions between several cytoskeletal and sarcomeric proteins. Nonsarcomeric ?-actinin-1 and ?-actinin-4 crosslink actin filaments in the cytoskeleton, while sarcomeric ?-actinin-2 and ?-actinin-3 serve a crucial role in anchoring actin filaments to the muscle Z-line. To assess the difference in turnover dynamics and structure/function properties between the ?-actinin isoforms at the sarcomeric Z-line, we used Fluorescence Recovery After Photobleaching (FRAP) in primary myofiber cultures. We found that the recovery kinetics of these proteins followed three distinct patterns: ?-actinin-2/?-actinin-3 had the slowest turn over, ?-actinin-1 recovered to an intermediate degree, and ?-actinin-4 had the fastest recovery. Interestingly, the isoforms' patterns of recovery were reversed at adhesion plaques in fibroblasts. This disparity suggests that the different ?-actinin isoforms have unique association kinetics in myofibers and that nonmuscle isoform interactions are more dynamic at the sarcomeric Z-line. Protein domain-specific investigations using ?-actinin-2/4 chimeric proteins showed that differential dynamics between sarcomeric and nonmuscle isoforms are regulated by cooperative interactions between the N-terminal actin-binding domain, the spectrin-like linker region and the C-terminal calmodulin-like EF hand domain. Together, these findings demonstrate that ?-actinin isoforms are unique in binding dynamics at the Z-line and suggest differentially evolved interactive and Z-line association capabilities of each functional domain.

SUBMITTER: Hsu CP 

PROVIDER: S-EPMC5943145 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature