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The B2 alternatively spliced isoform of nonmuscle myosin II-B lacks actin-activated MgATPase activity and in vitro motility
Authors:Kim Kye-Young  Kawamoto Sachiyo  Bao Jianjun  Sellers James R  Adelstein Robert S
Institution:a Laboratory of Molecular Cardiology, National Heart, Lung, and Blood Institute, National Institutes of Health Bethesda, MD 20892, USA
b Cardiology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health Bethesda, MD 20892, USA
c Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, National Institutes of Health Bethesda, MD 20892, USA
Abstract: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 20 kDa 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.
Keywords:aa  amino acid  NMHC  nonmuscle myosin heavy chain  HMM  heavy meromyosin  MHC  myosin heavy chain  MLC  myosin light chain  MLCK  myosin light chain kinase  IVM  in vitro motility
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