title: Functional characterization of the human myosin-7a motor domain.
abstract: Myosin-7a participates in auditory and visual processes. Defects in MYO7A, the gene encoding the myosin-7a heavy chain, are causative for Usher syndrome 1B, the most frequent cause of deaf-blindness in humans. In the present study, we performed a detailed kinetic and functional characterization of the isolated human myosin-7a motor domain to elucidate the details of chemomechanical coupling and the regulation of motor function. A rate-limiting, slow ADP release step causes long lifetimes of strong actin-binding intermediates and results in a high duty ratio. Moreover, our results reveal a Mg(2+)-sensitive regulatory mechanism tuning the kinetic and mechanical properties of the myosin-7a motor domain. We obtained direct evidence that changes in the concentration of free Mg(2+) ions affect the motor properties of human myosin-7a using an in vitro motility assay system. Our results suggest that in a cellular environment, compartment-specific fluctuations in free Mg(2+) ions can mediate the conditional switching of myosin-7a between cargo moving and tension bearing modes.
authors.affiliation: Institut für Biophysikalische Chemie, Medizinische Hochschule Hannover, Hannover, Germany. sarah.heissler@nih.gov
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Heissler
authors.forename: Dietmar J
authors.initials: DJ
authors.lastname: Manstein
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism; D000081412:Myosin VIIa; D009218:Myosins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000199:Actins; C000631455:MYO7A protein, human; D000081412:Myosin VIIa; D000244:Adenosine Diphosphate; D009218:Myosins; D008274:Magnesium