MYL10

Model summary

A cytosolic regulatory light chain that binds myosin and uses a paired EF-hand module to sense calcium and stabilize actomyosin assemblies central to smooth muscle contraction. By coupling calcium-dependent conformational changes with phosphorylation-sensitive interactions, it tunes filament assembly and contractile output. Its soluble nature places it primarily in the cytosol, with transient association to mitochondria that supports local energy supply during sustained contractility.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   The core scaffold is IPR011992 (EF-hand domain pair, residues 37–222), indicating a tandem EF-hand arrangement that typically forms a compact calcium-sensing and protein-binding module. Within this scaffold lie two discrete EF-hand domains annotated by IPR002048 (EF-hand domain, residues 84–119 and residues 154–189). The first EF-hand contains a defined calcium-coordination signature captured by IPR018247 (EF-Hand 1, calcium-binding site, residues 97–109), which predicts Ca2+-dependent conformational switching. The entire polypeptide is classified by IPR050403 (Myosin regulatory light chain family, residues 29–225), which specifies its role as the regulatory light chain that clamps onto the IQ motif of myosin heavy chains and tunes myosin filament assembly and activity. The ordered layout—an EF-hand pair embedded in a myosin light chain family framework—causes a Ca2+-responsive, high-affinity protein-binding surface that stabilizes and regulates myosin-based contractile machinery.

2. 02

   From this architecture, the molecular function resolves as multivalent protein binding (GO:0005515).

   EF-hand pairs in myosin light chains act primarily as conformational adaptors rather than catalytic centers; they bind myosin heavy chains and associated regulators, and their paired EF-hands provide a switchable interface that modulates filament assembly and actomyosin interactions.

3. 03

   This binding function directly drives smooth muscle contraction (GO:0006939).

   By stabilizing myosin regulatory ensembles and coupling Ca2+ signals to filament dynamics, the light chain promotes the assembly and performance of actomyosin complexes that generate force in visceral smooth muscle. The EF-hand pair’s Ca2+-sensing capacity integrates with phosphorylation pathways to tune cross-bridge cycling and filament stability, thereby controlling contractile output.

4. 04

   Cellular placement follows from the soluble EF-hand scaffold and absence of transmembrane features, pointing to a cytosolic pool (GO:0005829 cytosol).

   In smooth muscle cells, cytosolic myosin assemblies concentrate near energy-supplying organelles; transient association with mitochondria is therefore expected and aligns with a mitochondrial fraction (GO:0005739 mitochondrion). This positioning supports high ATP turnover and spatial coupling between contractile complexes and metabolic hubs.

5. 05

   Mechanistically, the EF-hand pair binds Ca2+ and shifts the conformation of the myosin light-chain interface, tightening or loosening contacts with myosin IQ motifs and thereby regulating filament assembly and actomyosin stability.

   I hypothesize that this light chain nucleates assemblies with non-muscle and smooth muscle myosins and their regulators. Likely partners include myosin heavy chains (e.g., smooth muscle myosin and non-muscle myosins), kinases and phosphatases that tune light-chain phosphorylation, and mitochondrial surface proteins that tether contractile complexes to energy-producing compartments. Together, these interactions create a Ca2+-tuned, phosphorylation-sensitive module that orchestrates smooth muscle contractility from a predominantly cytosolic locale with dynamic mitochondrial coupling.