Binding of myosin essential light chain to the cytoskeleton-associated protein IQGAP1

The 190 kD human IQGAP1 protein, by virtue of its N-terminal calponin-homology domain, is found associated with the actin cytoskeleton, and is capable of cross-linking actin filaments. IQGAP1 complexes with several proteins, including the Rho family GTPases Cdc42 and Rac, as well as calmodulin. It was previously noted that one of the IQ motifs of IQGAP1 displays significant similarity to a myosin heavy chain IQ motif responsible for binding the calmodulin-related myosin essential light chain (ELC). Employing the yeast two-hybrid methodology as well as in vitro binding experiments, we present evidence that a truncated version of IQGAP1 can interact with the myosin ELC. This interaction may have significant consequences for various cellular processes that involve actomyosin contractility, and suggests that the biological targets of the ELC may not be restricted to the myosin heavy chain.