MYL2

MYL2 encodes the ventricular myosin regulatory light chain (MLC-2v), which binds the flexible neck region of the myosin heavy chain in the hexameric sarcomeric myosin and thereby governs cross-bridge cycling kinetics, calcium-dependent contractile force, and the equilibrium between super-relaxed (SRX) and disordered-relaxed (DRX) myosin states (PMID:23365102, PMID:35177471). Phosphorylation of MYL2 at Ser15 by myosin light chain kinase tunes cross-bridge cycling and calcium-dependent contraction, displaying a transmural gradient (high epicardium, low endocardium), and the GATA4–MYLK3–MYL2 transcriptional/phosphorylation axis sets the steady-state level of this modification (PMID:26074085, PMID:41330421). Distinct missense substitutions derange sarcomere mechanics in opposite directions: the HCM-associated D166V mutation increases calcium sensitivity of force and shifts myosin out of the energy-conserving SRX state toward a hypercontractile DRX state, whereas the DCM-associated D94A mutation reduces RLC α-helical content and myosin incorporation, alters actin-activated ATPase, and favors the SRX state, producing a hypocontractile, dilated phenotype (PMID:25825243, PMID:29463717, PMID:35177471). Restoring Ser15 phosphorylation via phosphomimetic S15D rescues contractile and relaxation defects in HCM-D166V hearts, demonstrating the causal role of this regulatory site (PMID:31101927). Recessive loss-of-function and frameshift variants that disrupt the second EF-hand domain and heavy-chain binding—some triggering proteasomal degradation or mislocalization of the mutant protein—cause cardioskeletal myopathy, and pathogenic variants map preferentially to myosin interacting-heads-motif and heavy-chain interfaces of the thick filament (PMID:23365102, PMID:32453731). Beyond the sarcomere, MYL2 acts upstream of NLRP3 inflammasome activation and caspase-1–dependent pyroptosis in cardiac ischemia–reperfusion injury (PMID:40754120).

1. 1992 Medium

   Establishing the chromosomal location and a basic regulatory role for MYL2 provided the genomic foothold for later disease-gene mapping.

   Evidence Somatic cell hybrid Southern blot and in situ hybridization placing MYL2 at 12q23-q24.3

   PMID:1386340

   Open questions at the time

   • No functional mechanism beyond noting regulation of myosin ATPase
   • No mutation-phenotype link yet
2. 2013 Medium

   Defining MYL2 as the regulatory light chain bound to the myosin neck and linking EF-hand-disrupting recessive loss-of-function to cardioskeletal myopathy fixed its structural role in muscle contraction.

   Evidence Linkage analysis, exome sequencing, and immunohistochemistry of patient muscle for a splice-site mutation

   PMID:23365102

   Open questions at the time

   • Biochemical consequences of EF-hand disruption not reconstituted
   • Skeletal vs cardiac contribution not dissected
3. 2015 High

   Reconstitution showed how a DCM mutation acts at the molecular level—weakening RLC structure, myosin incorporation, and altering ATPase—moving beyond genetic association to biochemical causation.

   Evidence Recombinant D94A RLC reconstituted into RLC-depleted porcine cardiac preparations with CD, actin-activated ATPase, and skinned-fiber force assays

   PMID:25825243

   Open questions at the time

   • In vivo cardiac consequences not yet tested
   • Effect on SRX state not assessed in this study
4. 2015 Medium

   Spatially resolved Ser15 phosphorylation by MLCK was tied to cross-bridge kinetics and calcium-dependent contraction, defining the regulatory modification of MYL2.

   Evidence Review synthesizing genetic mouse models, computational modeling, and phosphorylation assays

   PMID:26074085

   Open questions at the time

   • Review-level synthesis rather than single primary dataset
   • Kinase identity and upstream control not resolved here
5. 2018 High

   An in vivo transgenic model confirmed D94A causes dilated cardiomyopathy and linked the phenotype to reduced ATPase, rightward force-pCa shift, and structural repositioning of cross-bridges—establishing a hypocontractile mechanism.

   Evidence D94A transgenic mice with echocardiography, hemodynamics, small-angle X-ray diffraction, ATPase and force-pCa measurements

   PMID:29463717

   Open questions at the time

   • SRX/DRX contribution clarified only in later work
   • Therapeutic reversibility not tested
6. 2016 High

   Characterizing a frameshift splice-site variant defined how C-terminal truncation impairs myosin and actin binding, ATPase, and contractile force, broadening the loss-of-function mechanism.

   Evidence Recombinant IVS6-1 RLC reconstituted into porcine cardiac preparations with ATPase, stopped-flow kinetics, and force/pCa assays

   PMID:27378946

   Open questions at the time

   • In vivo cardiac phenotype not established
   • Relationship to recessive myopathy variants not dissected
7. 2019 High

   Phosphomimetic rescue demonstrated that Ser15 phosphorylation is functionally decisive, converting a regulatory observation into a therapeutic principle for MYL2-driven HCM.

   Evidence AAV9 delivery of S15D-RLC into HCM-D166V transgenic mice with hemodynamics, strain, and skinned-fiber force

   PMID:31101927

   Open questions at the time

   • Durability and off-target effects of gene therapy not addressed
   • Applicability to other MYL2 mutations untested
8. 2019 Medium

   Patient-derived iPSC-cardiomyocytes connected an HCM MYL2 mutation to disrupted calcium handling and L-type channel current, extending pathology to excitation-contraction coupling.

   Evidence R58Q iPSC-CMs with calcium imaging, patch-clamp electrophysiology, and morphometry

   PMID:30796699

   Open questions at the time

   • Mechanistic link between RLC and ICa,L reduction unresolved
   • Single-cell model lacks tissue-level context
9. 2020 Medium

   Variant-specific fates—proteasomal degradation of a frameshift allele versus mislocalization of stable missense/stop-gain proteins—explained how different MYL2 alleles fail, with in vivo confirmation.

   Evidence Overexpression with proteasome-inhibitor rescue, patient-tissue immunohistochemistry, and Drosophila Mlc2 knockdown rescue

   PMID:32453731

   Open questions at the time

   • Degradation pathway components not identified
   • Quantitative contribution of mislocalization to human phenotype unknown
10. 2022 High

    Simultaneous X-ray diffraction, force, and ATP-turnover assays unified HCM and DCM mechanisms around the SRX/DRX equilibrium—D166V destabilizing SRX (hypercontractility) and D94A favoring SRX (hypocontractility).

    Evidence Skinned papillary muscle X-ray diffraction with isometric force and SRX/DRX ATP turnover assays in two transgenic mouse lines

    PMID:35177471

    Open questions at the time

    • How RLC mutations bias the IHM at atomic resolution not directly shown
    • Phosphorylation interplay with SRX not fully mapped
11. 2025 Medium

    A thick-filament cryo-EM model showed pathogenic HCM and DCM variants cluster at distinct myosin interacting-heads-motif and heavy-chain interfaces while benign variants avoid them, providing a structural framework for genotype interpretation.

    Evidence Cryo-EM atomic model of human cardiac thick filament with mapping of >200 variants and clinical outcome correlation (preprint)

    PMID:bio_10.1101_2025.10.03.680256

    Open questions at the time

    • Structural inference not validated by per-variant mutagenesis
    • Preprint, not peer-reviewed
12. 2025 Medium

    Identifying MYL2 as a direct tetramethylpyrazine target acting upstream of NLRP3 revealed a non-sarcomeric, inflammatory-protective role in ischemia-reperfusion injury.

    Evidence DARTS/LC-MS/MS target identification, siRNA knockdown epistasis, NLRP3 pharmacology, and in vitro/in vivo I-R models

    PMID:40754120

    Open questions at the time

    • Molecular link between MYL2 and NLRP3 not defined
    • Whether the effect is sarcomere-independent unclear
13. 2026 Medium

    Mapping a GATA4–MYLK3–MYL2 axis explained drug-induced reversible cardiotoxicity as loss of MYL2 phosphorylation, linking transcriptional control of the kinase to sarcomere function.

    Evidence iPSC-CM model, snRNA-seq of mouse heart, transverse aortic constriction in vivo, and omecamtiv pharmacological rescue

    PMID:41330421

    Open questions at the time

    • Direct GATA4 occupancy at MYLK3 not detailed here
    • Generalizability beyond osimertinib not established

• How MYL2 mechanistically couples to NLRP3 inflammasome signaling and to L-type calcium channel regulation, distinct from its sarcomeric role, remains unresolved.
• No molecular intermediary between MYL2 and NLRP3 identified
• Mechanism linking RLC mutation to ICa,L reduction unknown
• Phosphorylation-IHM-SRX interplay not resolved at atomic resolution