Myosin regulatory chain

Smooth muscle myosin contains two myosin light chains. Phosphorylation of the regulatory light chain by myosin light chain kinase is a mandatory step to induce contraction. 

The regulatory light chains from vertebrate forms of myosin-II undergo reversible phosphorylation by a calmodulin dependent enzyme called myosin light chain... 

The calcium mediated contraction of smooth muscle, which unlike striated muscle does not contain troponin, is quite different and requires a particular calcium-binding protein called calmodulin. Calmodulin (CM) is a widely distributed regulatory protein able to bind, with high affinity, four Ca2+ per protein molecule. The calcium—calmodulin (CaCM) complex associates with, and activates, regulatory proteins, usually enzymes, in many different cell types in smooth muscle the target regulatory proteins are caldesmon (CDM) and the enzyme myosin light chain kinase (MLCK). As described below, CaCM impacts on both actin and myosin filaments. 

S ATP -I- myosin regulatory light chain <12-14> (<12-14> catalytic domain... 

Rapid phosphorylation of the other detected phosphoproteins does occur but no definite roles have yet been ascribed to them. The 33 kDa protein may be the S6 ribosomal protein involved in the control of protein synthesis. The 57 kDa protein has been identified as the regulatory suhunit of the cyclic AMP-dependent protein kinase [44]. Of the other proteins the 76, 43 and 20 kDa may be connected with the microfilaments (43 kDa actin, 76 kDa myosin light chain kinase and 20 kDa myosin light chain) but this must be further investigated. These proteins may only play a permissive role in. steroidogenesis. The fact that the pattern of protein phosphorylation is very similar after stimulation of protein kinase C with phorbol esters supports this because the latter only marginally increase steroidogenesis [18]. 

Bornhauser BC, Olsson P-A, Lindholm D. 2003. MSAP is a novel MIR-interacting protein that enhances neurite outgrowth and increases myosin regulatory light chain. J Biol Chem 278 35412-35420. 

Olsson P-A, Korhonen L, Mercer EA, Lindholm D. 1999. MIR is a novel ERM-like protein that interacts with myosin regulatory light chain and inhibits neurite outgrowth. J Biol Chem 274 36288-36292. 

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