Does calmodulin activate MLCK?
MLCK is activated by calmodulin in response to an increase in intracellular calcium. It then goes on to phosphorylate regulatory myosin light chains at residues serine 19 and threonine 18 [2][3]. These phosphorylations enhance the ATPase activity of actin-activated myosin and so promotes myosin-driven contraction.
What is the function of MLCK?
Abstract. Myosin light chain kinase (MLCK) plays a central role in regulating the actin-myosin interaction of smooth muscle. MLCK phosphorylates the light chain of myosin in the presence of Ca2+ and calmodulin (CaM) thereby activating myosin so that it can interact with actin.
What is MLCK in smooth muscle?
The smooth muscle isoform of myosin light chain kinase (MLCK) is a Ca2+-calmodulin-activated kinase that is found in many tissues. It is particularly important for regulating smooth muscle contraction by phosphorylation of myosin.
What does protein kinase A do to MLCK?
Phosphorylation of MLCK at serine 1760 (‘regulatory site A’) by Ca2+/CaM-dependent protein kinase II (CaMK II) or protein kinase A (PKA) is known to regulate (decrease) the affinity of MLCK for Ca2+/CaM.
How is MLCK inactivated?
MLCK of both types are maintained in an inactive state through the binding of an autoinhibitory domain to the catalytic domain. Specifically, the autoinhibitory domain binds to the protein substrate-binding site but does not prevent binding of ATP.
Does protein kinase A phosphorylate MLCK?
Myosin light-chain kinase also known as MYLK or MLCK is a serine/threonine-specific protein kinase that phosphorylates a specific myosin light chain, namely, the regulatory light chain of myosin II.
Where is MLCK located?
MLCK is a Ser/Thr-kinase and phosphorylates a specific site near the N-terminus of the regulatory light chain (RLC) of the motor protein myosin-II.
What happens when MLCK is phosphorylated?
The phosphorylation of MLC will enable the myosin crossbridge to bind to the actin filament and allow contraction to begin (through the crossbridge cycle). Since smooth muscle does not contain a troponin complex, as striated muscle does, this mechanism is the main pathway for regulating smooth muscle contraction.
How does cAMP inhibit MLCK?
Unlike cardiac muscle, increased cAMP in smooth muscle causes relaxation. The reason for this is that cAMP normally inhibits myosin light chain kinase, the enzyme that is responsible for phosphorylating smooth muscle myosin and causing contraction. Like the heart, the cAMP is broken down by a cAMP-dependent PDE (PDE3).
What does calmodulin activate?
Calmodulin binds calcium and magnesium, and various calcium-calmodulin complexes bind to and activate both enzymes that regulate cellular calcium or cyclic nucleotides and specific protein kinases that regulate target enzymes by ATP-dependent phosphorylation.
Is phosphorylated MLCK active or inactive?
inactive state
MLCK of both types are maintained in an inactive state through the binding of an autoinhibitory domain to the catalytic domain.
How does calmodulin regulate calcium?
Calmodulin, an important Ca2+-binding protein, is a small acidic protein and is responsible for the regulation of intracellular Ca2+ levels. Increased Ca2+ concentration activates calmodulin that then induces specific kinases.
How does calmodulin help muscle contraction?
The overall result of this protein-protein interaction is a physiological effect, e.g., Ca2+ binding to calmodulin in smooth muscle allows it to interact with and activate myosin light chain kinase which catalyzes the phosphorylation of myosin. This reaction results in contraction of the smooth muscle.