Role of insert-1 of myosin VI in modulating nucleotide affinity.

Myosin VI is unique in its directionality among myosin superfamily members and also displays a slow and strain-dependent rate of ATP binding that allows for gating between its heads. In this study we demonstrate that leucine 310 is positioned by a class VI-specific insert, insert-1, so as to account for the selective hindrance of ATP versus ADP binding. Mutation of leucine 310 to glycine removes all influence of insert-1 on ATP binding. Furthermore, by analyzing myosin VI structures with either leucine 310 substituted to a glycine or complete removal of insert-1, we conclude that nucleotides may initially bind to myosin by their purine rings before docking their phosphate moieties. Otherwise, insert-1 could not exert a differential influence on ATP versus ADP binding.