C-terminal isoforms of the myosin heavy chain and smooth muscle function
Abstract
Two myosin heavy chain isoforms expressed in smooth muscle, SM1 (204 kDa) and SM2 (200 kDa), are derived from alternate splicing that results in different amino acid sequences at their non-helical C-terminal tail regions. These isoforms are developmentally regulated and differentially expressed in various smooth muscle tissues. The functional role of myosin isoforms differing at the C-terminal tail has been investigated both in vitro and in vivo. Removal of the C-terminal tail of SM1 by chymotrypsin activates the ATPase of myosin at low Mg2+ but does not change the maximum activity. Addition of peptides, mimicking C-terminal tail regions specific to the SM1 and SM2 isoforms, to permeabilized taenia coli smooth muscle fibers inhibits maximum shortening velocity (Vm) and decreases Ca2+ sensitivity but has no effect on maximum force. The inhibition of Vm by the SM1-peptide was not reversed on washout, whereas Vm inhibition by the SM2-peptide is reversible. We demonstrated that the SM1 peptide specifically bound to myosin at the subfragment 2-light meromyosin (S2-LMM) junction using crosslinking and immunomicroscopy. Modification at this site could have a direct effect on crossbridge function. The relation between C-terminal myosin...Continue Reading
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Contractile properties during development of hypertrophy of the smooth muscle in the rat portal vein
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Alternative splicing
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