Myosin V: regulation by calcium, calmodulin, and the tail domain.
Calcium activates the ATPase activity of tissue-purified myosin V, but not that of shorter expressed constructs. Here, we resolve this discrepancy by comparing an expressed full-length myosin V (dFull) to three shorter constructs. Only dFull has low ATPase activity in EGTA, and significantly higher activity in calcium. Based on hydrodynamic data and electron microscopic images, the inhibited state is due to a compact conformation that is possible only with the whole molecule. The paradoxical finding that dFull moved actin in EGTA suggests that binding of the molecule to the substratum turns it on, perhaps mimicking cargo activation. Calcium slows, but does not stop the rate of actin movement if excess calmodulin (CaM) is present. Without excess CaM, calcium binding to the high affinity sites dissociates CaM and stops motility. We propose that a folded-to-extended conformational change that is controlled by calcium and CaM, and probably by cargo binding itself, regulates myosin V's ability to transport cargo in the cell.
Dept. of Molecular Physiology and Biophysics, University of Vermont, 130 Health Science Research Facility, Burlington, VT 05405-0068, USA.
Dimitry N
DN
Krementsov
Elena B
EB
Krementsova
Kathleen M
KM
Trybus
D000199:Actins / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D002614:Chelating Agents / Q000378:metabolism; D004533:Egtazic Acid / Q000378:metabolism; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000378:metabolism; D024701:Myosin Type V / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012492:Salts / Q000737:chemistry; D014461:Ultracentrifugation; D014982:Xenopus laevis
D000199:Actins; D002147:Calmodulin; D002614:Chelating Agents; D020409:Molecular Motor Proteins; D012492:Salts; D004533:Egtazic Acid; D000251:Adenosine Triphosphatases; D024701:Myosin Type V; D002118:Calcium