Myosin light chain 9 (MYL9)

Myosin light chain 20 (MLC20), primarily encoded by the MYL9 gene in humans, is the 20 kDa regulatory light chain (RLC) associated with the myosin II motor protein. It serves as the primary molecular switch for initiating contraction in smooth muscle and regulating actomyosin dynamics in non-muscle cells (UniProt P24844). The biological activity of myosin is governed by the phosphorylation of MLC20 at Ser19 and Thr18, which is mediated by Myosin Light Chain Kinase (MLCK) in a calcium-dependent manner or by Rho-associated protein kinase (ROCK) (PubMed: 15640465). This phosphorylation increases myosin ATPase activity and promotes the assembly of myosin into filaments, leading to cellular contraction and force generation. In disease states, hyperphosphorylation of MLC20 is a hallmark of vascular hyper-reactivity in hypertension and airway constriction in asthma (PubMed: 23585134). Furthermore, MLC20-mediated contractility is essential for cancer cell migration and invasion, making it a focal point for anti-metastatic research. While few drugs bind MLC20 directly, it is a critical downstream effector for several approved and experimental drugs, such as Fasudil, which act by inhibiting the kinases responsible for its activation (DrugBank DB02114).

Other names

MLC20Myosin light chain 20Myosin regulatory light chain 9MLC-2RLCLC20Myosin light chain 2, smooth muscle and non-muscle

Inhibition of phosphorylation at Ser-19 and Thr-18 by targeting upstream kinases (MLCK or ROCK) or activating myosin light chain phosphatase (MLCP) to induce smooth muscle relaxation and inhibit cell motility.