Myosin Regulatory Light Chain MRCL3 (11-24)

Product Name: Myosin Regulatory Light Chain MRCL3 (11-24)

Sequence One Letter Code: KKRPQRATSNVFAM-NH2

Sequence Three Letter Code: H-Lys-Lys-Arg-Pro-Gln-Arg-Ala-Thr-Ser-Asn-Val-Phe-Ala-Met-NH2

Chemical Formula:C70H121N25O18S1

Molecular Weight: 1633

Purity: 95%

Form: Lyophilized

Storage Conditions: - 20 °C

Research Area: peptide substrate

Source / Species: Human, mouse, rat, bovine, zebrafish

Conjugation: Unconjugated

Code Nacres: NA.26

Application: MRCL3 (11–24) is a synthetic peptide derived from residues 11–24 of the human myosin regulatory light chain. It serves as a substrate for myosin light chain kinase (MLCK), a key regulator of actomyosin contractility and cytoskeletal organization. Phosphorylation of this region modulates muscle contraction, cell motility, and barrier function. The peptide is commonly used in biochemical assays to measure MLCK activity, assess kinase specificity, and study phosphorylation-dependent regulation of cytoskeletal dynamics. It supports research into smooth muscle physiology, endothelial permeability, and signaling pathways controlling cellular contractility and migration.

Current Research: Myosin regulatory light chain (MRLC), also known as myosin light chain 2 (MLC2), is a central regulatory component of the actomyosin cytoskeleton. Phosphorylation of MRLC by myosin light chain kinase (MLCK) enhances actin-activated myosin ATPase activity, promotes myosin filament assembly, and drives contractile force generation in both muscle and non-muscle cells. MRCL3 (11–24) is a synthetic peptide corresponding to residues 11–24 of the human myosin regulatory light chain and contains the critical phosphorylation site targeted by MLCK. As a defined biochemical substrate, it is widely used to quantify MLCK catalytic activity and to study phosphorylation-dependent control of cytoskeletal dynamics. The 11–24 region of MRLC encompasses the conserved serine residue (Ser19 in the full-length protein) that is phosphorylated by MLCK in a Ca²⁺/calmodulin-dependent manner. In smooth muscle and many non-muscle cell types, MLCK activation follows intracellular Ca²⁺ elevation, which promotes calmodulin binding and conformational activation of the kinase. Phosphorylation of MRLC at Ser19, and in some contexts Thr18, increases actomyosin contractility by enhancing cross-bridge cycling and stabilizing myosin filament interactions with actin. The MRCL3 (11–24) peptide recapitulates this phosphorylation motif in a minimal format, allowing direct and reproducible measurement of MLCK activity in vitro. In biochemical kinase assays, MRCL3 (11–24) serves as a soluble and structurally defined substrate. Recombinant MLCK is incubated with the peptide in the presence of ATP and Ca²⁺/calmodulin, and phosphorylation is quantified using radiometric detection, phospho-specific antibodies, fluorescence-based readouts, or mass spectrometry. This format enables determination of kinetic parameters such as Km and kcat, providing insight into enzyme efficiency and substrate recognition. Because the peptide lacks higher-order structural complexity, it allows precise analysis of catalytic activity independent of filament assembly or additional regulatory domains present in the full-length protein. The peptide is also used to assess MLCK isoform specificity and to distinguish MLCK activity from other kinases capable of phosphorylating MRLC, such as Rho-associated kinase (ROCK) or zipper-interacting protein kinase (ZIPK). By combining MRCL3 (11–24) phosphorylation assays with selective inhibitors or recombinant kinase variants, researchers can dissect pathway contributions to contractile regulation. This is particularly important in cellular systems where multiple kinases converge on the same phosphorylation site. In smooth muscle physiology, MLCK-mediated phosphorylation of MRLC regulates vascular tone, gastrointestinal motility, airway constriction, and uterine contraction. Dysregulation of MLCK activity has been implicated in hypertension, asthma, and other contractility-related disorders. MRCL3 (11–24)-based assays support pharmacological screening of MLCK inhibitors aimed at modulating smooth muscle contractile responses. Quantitative evaluation of inhibitor potency and mechanism of action relies on defined substrates such as this peptide. Beyond muscle tissues, MLCK plays a critical role in non-muscle cells, where it controls cytoskeletal tension, cell migration, and intercellular junction integrity. In endothelial cells, phosphorylation of MRLC promotes actomyosin contraction and increases paracellular gap formation, contributing to enhanced vascular permeability. In inflammatory states, MLCK activation is associated with barrier dysfunction and tissue edema. The MRCL3 (11–24) peptide supports mechanistic studies investigating how inflammatory mediators, growth factors, or mechanical stress regulate MLCK activity and downstream cytoskeletal remodeling. Cell motility and cancer metastasis research also benefit from MLCK substrate assays. Actomyosin contractility is essential for cell migration, focal adhesion turnover, and invasive behavior. By measuring MLCK activity toward MRCL3 (11–24), researchers can evaluate how signaling pathways such as RhoA/ROCK, Ca²⁺ flux, or growth factor stimulation influence contractile machinery activation. These insights contribute to understanding how cytoskeletal dynamics are coordinated during tissue morphogenesis and tumor progression. In summary, MRCL3 (11–24) is a synthetic peptide encompassing the key phosphorylation motif of the human myosin regulatory light chain and serves as a defined substrate for MLCK. Its use in quantitative kinase assays enables detailed analysis of enzyme kinetics, specificity, and inhibitor activity. By supporting investigations into smooth muscle contraction, endothelial barrier regulation, and cell migration, this peptide remains an essential tool for studying phosphorylation-dependent control of cytoskeletal organization and cellular contractility.