9SIR

THE CRYSTAL STRUCTURE OF HUMAN MUSCLE ALPHA-ACTININ-2 Mutant R327C

Summary for 9SIR

• Entry DOI: 10.2210/pdb9sir/pdb
• Descriptor: Alpha-actinin-2 (1 entity in total)
• Functional Keywords: contractile protein, z-disc, calmodulin-like domain, spectrin domain, actin binding domain, abd
• Biological source: Homo sapiens (human)
• Total number of polymer chains: 1
• Total formula weight: 99926.46

Authors

Noureddine, M.,Pinotsis, N.,Mikolajek, H.,Gehmlich, K.,Mohammed, F. (deposition date: 2025-08-29, release date: 2026-07-29, Last modification date: 2026-08-05)

Primary citation

Noureddine, M.,Mikolajek, H.,Cowieson, N.,Pinotsis, N.,Robinson, P.,Slater, A.,Redwood, C.,Loughna, S.,Denning, C.,Mohammed, F.,Gehmlich, K.
Comprehensive biophysical and structural profiling of alpha-actinin-2 variants reveals mechanistic diversity in hypertrophic cardiomyopathy.
Nat Commun, 17:-, 2026

PubMed Abstract: Hypertrophic cardiomyopathy (HCM) is a genetic disease associated with sudden cardiac death. Variants in alpha-actinin-2 (ACTN2), a Z-disc protein that anchors actin thin filaments have been implicated in HCM, yet their structural consequences remain poorly defined. Here, we characterise seventeen HCM-associated ACTN2 variants spanning multiple domains using an integrated and tiered workflow combining high-throughput assays, structural modelling and biophysical approaches. All variants display reduced solubility, with actin-binding domain (ABD) substitutions showing pronounced thermal instability by differential scanning fluorimetry. Modelling of nine variants predicts diverse pathogenic mechanisms including compromised actin-binding, impaired ABD regulatory conformations, disrupted dimerisation interfaces, and perturbed domain architecture. Crystal structures of two rod-domain variants reveal intact dimerisation despite modelling predictions. Actin-binding assays for ABD variants confirm altered actin engagement suggesting that binding dynamics may drive pathogenicity. Limited proteolysis indicates reduced structural stability across variants, while size-exclusion chromatography coupled with multi-angle light scattering or small-angle X-ray scattering (SEC-MALS/SAXS) shows a strong propensity for aggregation. Batch-mode SAXS further demonstrates early aggregation onset in selected ABD variants at elevated temperatures. Collectively, these findings establish that HCM-linked ACTN2 variants compromise protein integrity through multiple mechanisms, highlight the ABD as a hotspot of vulnerability and provide a potential framework for interpreting cardiomyopathy-associated variants.

PubMed: 42481460
DOI: 10.1038/s41467-026-75392-z

Experimental method

X-RAY DIFFRACTION (3.7 Å)