An alternatively spliced isoform of non-muscle myosin II-C is not regulated by myosin light chain phosphorylation.
We report a novel isoform of non-muscle myosin II-C (NM II-C), NM II-C2, that is generated by alternative splicing of an exon, C2, encoding 41 amino acids in mice (33 in humans). The 41 amino acids are inserted into loop 2 of the NM II-C heavy chain within the actin binding region. Unlike most vertebrate non-muscle and smooth muscle myosin IIs, baculovirus-expressed mouse heavy meromyosin (HMM) II-C2 demonstrates no requirement for regulatory myosin light chain (MLC(20)) phosphorylation for maximum actin-activated MgATPase activity or maximum in vitro motility as measured by the sliding actin filament assay. In contrast, noninserted HMM II-C0 and another alternatively spliced isoform HMM II-C1, which contains 8 amino acids inserted into loop 1, are dependent on MLC(20) phosphorylation for both actin-activated MgATPase activity and in vitro motility ( Kim, K. Y., Kovacs, M., Kawamoto, S., Sellers, J. R., and Adelstein, R. S. (2005) J. Biol. Chem. 280, 22769-22775 ). HMM II-C1C2, which contains both the C1 and C2 inserts, does not require MLC(20) phosphorylation for full activity similar to HMM II-C2. These constitutively active C2-inserted isoforms of NM II-C are expressed only in neuronal tissue. This is in contrast to NM II-C1 and NM II-C0, both of which are ubiquitously expressed. Full-length NM II-C2-GFP expressed in COS-7 cells localizes to filaments in interphase cells and to the cytokinetic ring in dividing cells.
Jana
Siddhartha S
SS
Laboratory of Molecular Cardiology and Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA. bcssj@iacs.res.in
Kim
Kye-Young
KY
Mao
Jian
J
Kawamoto
Sachiyo
S
Sellers
James R
JR
Adelstein
Robert S
RS
D000199:Actins / Q000737:chemistry; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004305:Dose-Response Relationship, Drug; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D018994:Myosin Light Chains / Q000737:chemistry*; D024462:Myosin Type II / Q000737:chemistry*; D009474:Neurons / Q000378:metabolism; D010766:Phosphorylation; D017386:Sequence Homology, Amino Acid
D000199:Actins; D018994:Myosin Light Chains; D049452:Green Fluorescent Proteins; D024462:Myosin Type II