Functional divergence of human cytoplasmic myosin II: kinetic characterization of the non-muscle IIA isoform.
Cytoplasmic (or non-muscle) myosin II isoforms are widely expressed molecular motors playing essential cellular roles in cytokinesis and cortical tension maintenance. Two of the three human non-muscle myosin II isoforms (IIA and IIB) have been investigated at the protein level. Transient kinetics of non-muscle myosin IIB showed that this motor has a very high actomyosin ADP affinity and slow ADP release. Here we report the kinetic characterization of the non-muscle myosin IIA isoform. Similar to non-muscle myosin IIB, non-muscle myosin IIA shows high ADP affinity and little enhancement of the ADP release rate by actin. The ADP release rate constant, however, is more than an order of magnitude higher than the steady-state ATPase rate. This implies that non-muscle myosin IIA spends only a small fraction of its ATPase cycle time in strongly actin-bound states, which is in contrast to non-muscle myosin IIB. Non-muscle myosin II isoforms thus appear to have distinct enzymatic properties that may be of importance in carrying out their cellular functions.
Kovács
Mihály
M
Laboratory of Molecular Cardiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1762, USA.
Wang
Fei
F
Hu
Aihua
A
Zhang
Yue
Y
Sellers
James R
JR
D000199:Actins / Q000378:metabolism; D000205:Actomyosin / Q000737:chemistry; D000244:Adenosine Diphosphate / Q000737:chemistry; D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008958:Models, Molecular; D024507:Nonmuscle Myosin Type IIA / Q000737:chemistry* / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms; D013050:Spectrometry, Fluorescence; D013997:Time Factors
D000199:Actins; D018076:DNA, Complementary; D010710:Phosphates; D020033:Protein Isoforms; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000205:Actomyosin; D000251:Adenosine Triphosphatases; D024507:Nonmuscle Myosin Type IIA