The kinetic mechanism of Myo1e (human myosin-IC).
Myo1e is the widely expressed subclass-1 member of the myosin-I family. We performed a kinetic analysis of a truncated myo1e that consists of the motor and the single IQ motif with a bound calmodulin. We determined the rates and equilibrium constants for the key steps in the ATPase cycle. The maximum actin activated ATPase rate (V(max)) and the actin concentration at half-maximum of V(max) (K(ATPase)) of myo1e are similar to those of the native protein. The K(ATPase) is low (approximately 1 microm), however the affinity of myo1e for actin in the presence of ATP is very weak. A weak actin affinity and a rapid rate of phosphate release result in a pathway under in vitro assay conditions in which phosphate is released while myo1e is dissociated from actin. Actin activation of the ATPase activity and the low K(ATPase) are the result of actin activation of ADP release. We propose that myo1e is tuned to function in regions of high concentrations of cross-linked actin filaments. Additionally, we found that ADP release from actomyo1e is > 10-fold faster than other vertebrate myosin-I isoforms. We propose that subclass-1 myosin-Is are tuned for rapid sliding, whereas subclass-2 isoforms are tuned for tension maintenance or stress sensing.
El Mezgueldi
Mohammed
M
Department of Physiology and The Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6085, USA.
Tang
Nanyun
N
Rosenfeld
Steven S
SS
Ostap
E Michael
EM
D000199:Actins / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002147:Calmodulin / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008956:Models, Chemical; D008969:Molecular Sequence Data; D024461:Myosin Type I; D009218:Myosins / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology*; D011485:Protein Binding; D020033:Protein Isoforms; D011817:Rabbits; D013997:Time Factors
D000199:Actins; D002147:Calmodulin; D018076:DNA, Complementary; D020033:Protein Isoforms; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C511011:MYO1E protein, human; D024461:Myosin Type I; C460367:MYO1C protein, human; D009218:Myosins