An alpha-actinin binding site of zyxin is essential for subcellular zyxin localization and alpha-actinin recruitment.

The LIM domain protein zyxin is a component of adherens type junctions, stress fibers, and highly dynamic membrane areas and appears to be involved in microfilament organization. Chicken zyxin and its human counterpart display less than 60% sequence identity, raising concern about their functional identity. Here, we demonstrate that human zyxin, like the avian protein, specifically interacts with alpha-actinin. Furthermore, we map the interaction site to a motif of approximately 22 amino acids, present in the N-terminal domain of human zyxin. This motif is both necessary and sufficient for alpha-actinin binding, whereas a downstream region, which is related in sequence, appears to be dispensable. A synthetic peptide comprising human zyxin residues 21-42 specifically binds to alpha-actinin in solid phase binding assays. In contrast to full-length zyxin, constructs lacking this motif do not interact with alpha-actinin in blot overlays and fail to recruit alpha-actinin in living cells. When zyxin lacking the alpha-actinin binding site is expressed as a fusion protein with green fluorescent protein, association of the recombinant protein with stress fibers is abolished, and targeting to focal adhesions is grossly impaired. Our results suggest a crucial role for the alpha-actinin-zyxin interaction in subcellular zyxin localization and microfilament organization.