The B2 alternatively spliced isoform of nonmuscle myosin II-B lacks actin-activated MgATPase activity and in vitro motility.
We report the initial biochemical characterization of an alternatively spliced isoform of nonmuscle heavy meromyosin (HMM) II-B2 and compare it with HMM II-B0, the nonspliced isoform. HMM II-B2 is the HMM derivative of an alternatively spliced isoform of endogenous nonmuscle myosin (NM) II-B, which has 21-amino acids inserted into loop 2, near the actin-binding region. NM II-B2 is expressed in the Purkinje cells of the cerebellum as well as in other neuronal cells [X. Ma, S. Kawamoto, J. Uribe, R.S. Adelstein, Function of the neuron-specific alternatively spliced isoforms of nonmuscle myosin II-B during mouse brain development, Mol. Biol. Cell 15 (2006) 2138-2149]. In contrast to any of the previously described isoforms of NM II (II-A, II-B0, II-B1, II-C0 and II-C1) or to smooth muscle myosin, the actin-activated MgATPase activity of HMM II-B2 is not significantly increased from a low, basal level by phosphorylation of the 20kDa myosin light chain (MLC-20). Moreover, although HMM II-B2 can bind to actin in the absence of ATP and is released in its presence, it cannot propel actin in the sliding actin filament assay following MLC-20 phosphorylation. Unlike HMM II-B2, the actin-activated MgATPase activity of a chimeric HMM with the 21-amino acid II-B2 sequence inserted into the homologous location in the heavy chain of HMM II-C is increased following MLC-20 phosphorylation. This indicates that the effect of the II-B2 insert is myosin heavy chain specific.
Laboratory of Molecular Cardiology, National Heart, Lung, and Blood Institute, National Institutes of Health Bethesda, MD 20892, USA.
Kye-Young
KY
Kim
Sachiyo
S
Kawamoto
Jianjun
J
Bao
James R
JR
Sellers
Robert S
RS
Adelstein
D000199:Actins / Q000737:chemistry* / Q000648:ultrastructure; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase / Q000737:chemistry*; D004789:Enzyme Activation; D020409:Molecular Motor Proteins / Q000737:chemistry* / Q000648:ultrastructure; D009038:Motion; D018482:Muscle, Skeletal / Q000737:chemistry; D024501:Nonmuscle Myosin Type IIB / Q000737:chemistry* / Q000235:genetics* / Q000648:ultrastructure; D011485:Protein Binding; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry / Q000648:ultrastructure; D022821:RNA Splice Sites / Q000235:genetics; D013329:Structure-Activity Relationship
D000199:Actins; D020409:Molecular Motor Proteins; D020033:Protein Isoforms; D022821:RNA Splice Sites; D017301:Ca(2+) Mg(2+)-ATPase; D024501:Nonmuscle Myosin Type IIB