Actin binding domain of Rng2 sparsely bound on F-actin strongly inhibits actin movement on myosin II
AbstractThe contraction of contractile rings (CRs) depends on interaction between actin filaments and myosin II filaments. The rate of contraction in the fission yeast Schizosaccharomyces pombe is less than 1/120 of the velocity of acto-myosin II movement in vitro, but the mechanism of inhibition has not been described. Here, we found that the calponin-homology actin binding domain of fission yeast IQGAP Rng2 (Rng2CHD) strongly inhibits the motility of actin filaments on skeletal muscle myosin II fragments in vitro, even at a low ratio of bound Rng2CHD to actin protomers, reducing the sliding velocity to half when the binding ratio was 1/75. Rng2CHD also induced structural changes of actin filaments and reduced the affinity between actin filaments and subfragment 1 (S1) of muscle myosin II carrying ADP. Intriguingly, actin-activated ATPase of S1 was only mildly inhibited, even by high concentrations of Rng2CHD. Moreover, the motility of actin filaments by myosin V was not inhibited by Rng2CHD. We propose a new regulatory mechanism for acto-myosin II movement that involves Rng2CHD-induced structural changes of actin filaments.