Nonmuscle myosin class II proteins belong to the superfamily of actin-based motor proteins. They form hexamer structures composed of two ~200kDa heavy chains (NMHC II) and two pairs of 20kDa and 17kDa light chains (MLC20 and MLC17) (1,2). Nonmuscle myosins are classified according to the heavy chain isoforms; light chains are conserved. Three different isoforms that share 64-80% amino acid sequence identity have been detected in mammals: NMHC II-A, NMHC II-B, and NMHC II-C.
Although NMHC II molecules have now been found in muscle cells as well, the name “nonmuscle myosin” was already widespread and is in use today. NMHC II-A is most abundant compared to other NMHC isoforms in human lung, spleen, thymus, uterus, and colon.1 Thus, single amino acid mutation in MNMH II-A results in kidney and platelet defects in humans.1 In addition, recent study indicates that replacement of NMHC II-B with NMHC II-A rescues brain defect in mice.3
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1. Golomb E. et al. J. Biol. Chem. 279, 2800 (2004).
2. Conti MA. et al. J. of Cell Sci. 121, 11 (2007).
3. Bao J. et al. J. Biol. Chem. 282, 22102 (2007).