title: Conditional loss-of-myosin-II-function mutants reveal a position in the tail that is critical for filament nucleation.
abstract: Myosin-II must be assembled into filaments to perform its cellular functions. Two conditional loss-of-myosin-II-function mutants were recovered from a previous genetic screen with defects that were mapped to the coiled-coil tail region of Dictyostelium myosin-II. Strikingly, both tail mutations affected the same arginine residue at position 1880. A single amino acid substitution, R1880P, disrupted both the dimerization and tetramerization steps of filament nucleation. Even a single charge reversal at this position, R1880D, was sufficient to inhibit filament assembly, while other single charge reversals in the region of antiparallel contract suppressed these filament assembly mutants. The considerable impact of small electrostatic forces on nucleation suggests that these steps are delicately balanced and easily reversible.
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, California 94305, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Moores
authors.forename: J A
authors.initials: JA
authors.lastname: Spudich
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism*; D019943:Amino Acid Substitution; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001120:Arginine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004023:Dictyostelium / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D009154:Mutation / Q000235:genetics; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism; D015879:Myosin Subfragments / Q000235:genetics* / Q000502:physiology; D009218:Myosins / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D010766:Phosphorylation; D011392:Proline / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013912:Threonine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D000596:Amino Acids; D015879:Myosin Subfragments; D013912:Threonine; D001120:Arginine; D011392:Proline; D018995:Myosin Heavy Chains; D009218:Myosins