MYLK2

MYLK2 Full Name

myosin light chain kinase 2

MYLK2 Introduction

MYLK2, officially known as myosin light chain kinase 2, is a protein-coding gene located on chromosome 20q13.31 in humans. It belongs to the immunoglobulin (Ig) superfamily of serine/threonine-protein kinases, but it is uniquely restricted in its expression pattern. Unlike the ubiquitous smooth muscle myosin light chain kinase, MYLK2 is almost exclusively found in adult skeletal muscle fibers. This tissue-specific presence immediately hints at its specialized physiological role, rather than a general housekeeping function. The gene spans roughly 10 kilobases and produces a transcript that translates into a 579-amino-acid polypeptide, distinguishing it from its longer isoforms found in other muscle types.The MYLK2 protein adopts a compact, two-domain structure: a catalytic kinase core at the N-terminus and a regulatory calmodulin-binding motif near the C-terminus. Its kinase activity is strictly calcium-dependent, triggered when calmodulin binds to the regulatory region upon intracellular Ca²⁺ elevation. This binding relieves autoinhibition, allowing ATP to dock and phosphorylate the target substrate. The catalytic domain contains the conserved HRD (histidine-arginine-aspartate) and DFG (aspartate-phenylalanine-glycine) motifs typical of protein kinases, ensuring precise phosphate transfer. Unlike cardiac MLCK, MYLK2 lacks extensive N-terminal extensions, making it a streamlined, fast-responding enzyme suited for brief, high-intensity muscle contractions.

Figure 1.Mechanism of MYLK2.

Biological Substrate and Phosphorylation Target
MYLK2 specifically phosphorylates the regulatory light chain of myosin II, known as MLC2 (myosin light chain 2), at serine 15. This phosphorylation event is a critical switch for skeletal muscle contraction, as it increases the actin-activated ATPase activity of myosin cross-bridges. The modified light chain enhances the rate of force development during twitch and tetanic contractions, particularly in fast-twitch glycolytic fibers. Importantly, MYLK2 does not affect the relaxation phase; its action is restricted to the early contractile kinetics. This substrate selectivity is maintained through unique docking interactions between the kinase's surface loops and the N-terminal helix of MLC2, ensuring high fidelity in vivo.

Physiological Significance in Muscle Performance
In living organisms, MYLK2 modulates the speed and magnitude of skeletal muscle force generation. Animal studies reveal that its expression correlates positively with muscle fiber type—higher levels are found in type IIb/x fast fibers compared to slow oxidative type I fibers. During high-frequency stimulation, MYLK2-mediated phosphorylation accelerates cross-bridge cycling, enabling rapid power output for jumping or sprinting. Furthermore, it contributes to post-tetanic potentiation, a short-term memory-like effect that enhances subsequent twitch forces. Knockout models show reduced maximal shortening velocity without altering resting tension, confirming that MYLK2 fine-tunes dynamic performance rather than baseline tone or endurance.

Alternate Names for MYLK2

MYLK2; myosin light chain kinase 2; myosin light chain kinase 2, skeletal muscle; myosin light chain kinase 2, skeletal/cardiac muscle; KMLC; MLCK2; skeletal muscle myosin light chain kinase; skMLCK; MLCK;