(myosin-light-chain) phosphatase

In enzymology, a myosin light-chain phosphatase (MLCP) is an enzyme that catalyzes the chemical reaction


 * [myosin light-chain] phosphate + H2O $$\rightleftharpoons$$ [myosin light-chain] + phosphate

Thus, the two substrates of this enzyme are myosin light-chain phosphate and H2O, whereas its two products are myosin light-chain and phosphate.

This enzyme belongs to the family of hydrolases, specifically those acting on phosphoric monoester bonds. The systematic name of this enzyme class is [myosin-light-chain]-phosphate phosphohydrolase. Other names in common use include myosin light chain kinase phosphatase, myosin phosphatase, myosin phosphatase, protein phosphatase 2A, and myosin-light-chain-phosphatase.

Structural studies
MLCP is composed of three subunits: a PP1c catalytic subunit, a myosin targeting subunit called MYPT1, and a small subunit of unknown function called M20.

As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code.

Function
MLCP is important for regulating contraction in smooth muscle, which lacks the troponin binding system. It inhibits contraction by dephosphorylating myosin light-chain fibers. It counters the myosin light-chain kinase (MLCK), which promotes contraction by phosphorylating myosin light-chain proteins. MLCP is present in smaller amounts compared with MLCK, but compensates for this lack of mass by rapid movement along actin fibers. MLCP activity is inhibited by Rhoa and Rho kinase, components of the Ca2+ independent pathway for maintaining muscle contraction. This can result in Ca2+ sensitization.