The A31P missense mutation in cardiac myosin binding protein C alters protein structure but does not cause...

Area of Science:

• Cardiovascular Biology
• Molecular Genetics
• Protein Biochemistry

Background:

• Mutations in MYBPC3, encoding cardiac myosin binding protein C (cMyBP-C), are a primary cause of hypertrophic cardiomyopathy (HCM).
• Both premature stop codon mutations and missense mutations are common genetic alterations leading to HCM.

Purpose of the Study:

• To investigate the functional consequences of a specific missense mutation, alanine to proline at amino acid 31 (A31P), in the C0 domain of cMyBP-C.
• To determine the mechanism by which the A31P mutation causes HCM in cats.

Main Methods:

• Recombinant protein expression and structural analysis.
• Enzyme digestion assays (trypsin).
• Western blotting of myocardial tissue from affected cats.
• Immunohistochemical localization studies.

Main Results:

• The A31P mutation disrupted the structure of the C0 domain and altered its susceptibility to enzymatic digestion.
• Western blots revealed reduced levels of mutant A31P cMyBP-C relative to wild-type, but total cMyBP-C levels were unchanged, suggesting altered protein turnover.
• The mutant A31P cMyBP-C was correctly localized within cardiac sarcomeres.
• Haploinsufficiency due to reduced protein expression was ruled out as the primary cause of HCM.

Conclusions:

• The A31P mutation in cMyBP-C does not cause HCM through haploinsufficiency.
• The findings support a 'poison polypeptide' mechanism, where the mutant protein itself disrupts myocyte function and leads to hypertrophic cardiomyopathy.