title: Low ionic strength solubility of myosin in sea urchin egg extracts is mediated by a myosin-binding protein.
abstract: We identify a novel myosin-binding protein, designated 53K, which appears to mediate the low ionic strength solubility of myosin in extracts of unfertilized sea urchin eggs. The protein possesses a subunit molecular mass on SDS-PAGE of 53 kD, an S value of 7, may be organized into disulfide-linked oligomers, and is associated with myosin in egg extracts. Both myosin and 53K co-precipitate from extract upon the addition of nucleoside triphosphates and co-sediment with an S value of 24 by sedimentation velocity centrifugation. Myosin in extracts not associated with 53K has an S value of 10. Further, myosin can be immunoprecipitated from extract with antibody to 53K and the 53K in extracts binds to a myosin affinity column. When extract is depleted of 53K, a majority of the myosin precipitates out of extract in a nucleotide-independent manner. Whereas purified myosin precipitates in the absence of nucleotide when recombined with dialysis buffer or myosin-depleted extract, reconstituting 53K and myosin before addition to buffer or myosin-depleted extract partially restores the low ionic strength solubility demonstrated by myosin in fresh egg extracts. The 53-kD protein may represent a new class of authentic myosin-binding proteins that may regulate the supramolecular organization of myosin in nonmuscle cells.
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D005260:Female; D008854:Microscopy, Electron; D008970:Molecular Weight; D009218:Myosins / Q000378:metabolism*; D009994:Osmolar Concentration; D010063:Ovum / Q000502:physiology*; D010766:Phosphorylation; D012617:Sea Urchins; D012995:Solubility
chemical_list: D002352:Carrier Proteins; D009218:Myosins