MYL6

MYL6 Full Name

myosin, light chain 6, alkali, smooth muscle and non-muscle

MYL6 Introduction

MYL6, officially designated as myosin light chain 6, is a ubiquitous 17-kDa protein that belongs to the superfamily of EF-hand calcium-binding motifs. Unlike its striated muscle-specific counterparts, MYL6 is classified as an alkali light chain, predominantly expressed in smooth muscle and all non-muscle cell types. Its genetic locus is found on chromosome 12q13.2, a region frequently associated with transcriptional regulation during development. The protein shares high sequence homology with MYL6B, yet retains unique N-terminal acetylation patterns that influence its stability. Structurally, it is composed of four helix-loop-helix domains, though only one retains canonical calcium-binding capacity, making it a degenerate member of the calmodulin family with specialized mechanical roles.

Figure 1.MYL6 protein structure & domains.

Distinctive Nomenclature and Isoform Variants
This protein is widely recognized under multiple synonymous names, including MLC-3, LC17, and the essential light chain of smooth muscle myosin. In human databases, it is also cataloged as MLC1SM and MYL6A, reflecting historical discrepancies in cloning studies. Two major splice variants exist: isoform 1 (the longer cytoplasmic form) and isoform 3 (which lacks an internal exon), both generated from a single gene via alternative splicing. These variants exhibit tissue-dependent expression ratios, with the shorter form predominating in vascular endothelium. Furthermore, post-translational phosphorylation at serine 18 distinguishes functionally active pools from inactive reservoirs, adding another layer of complexity to its nomenclature and functional annotation in proteomic studies.

Physiological Significance in Smooth Muscle Tone
In smooth muscle tissues—such as those lining blood vessels, airways, and gastrointestinal tracts—MYL6 is indispensable for sustained tonic contraction without rapid fatigue. It cooperates with caldesmon and calponin to modulate actin-myosin cross-bridge cycling, particularly during the latch state, which conserves energy while maintaining long-term tension. Genetic knockdown studies in murine models demonstrate that reduced MYL6 expression leads to hypotensive phenotypes due to diminished vascular responsiveness to vasoconstrictors. Moreover, its expression is upregulated under hypoxic conditions, suggesting an adaptive role in preserving contractile function during metabolic stress. These findings position MYL6 as a potential therapeutic target for disorders like asthma and hypertension.

Alternate Names for MYL6

MYL6; myosin, light chain 6, alkali, smooth muscle and non-muscle; myosin, light polypeptide 6, alkali, smooth muscle and non muscle; myosin light polypeptide 6; ESMLC; MLC1SM; MLC3NM; myosin light chain A3; 17 kDa myosin light chain; myosin light chain alkali 3