Pyridoxine non-responsive p.R336C mutation alters the molecular properties of cystathionine beta-synthase leading to severe homocystinuria phenotype

• The prevalence of homocystinuria in Qatar is 1:1800, mainly due to a founder missense mutation p.R336C. • The cystathionine beta-synthase (CBS) R336C mutant was bacterially expressed, purified and its molecular properties were compared to CBS wild type (WT) recombinant protein. • Our data revealed that p.R336C mutation results in a dramatic reduction (∼86%) of CBS enzymatic activity. • Circular Dichroism experiments suggested that the p.R336C mutation does not significantly alter the secondary structure of the CBS protein. • CD spectra also revealed distinct differences in the thermal unfolding mechanisms of CBS WT and R336C mutant protein species. • Chemical denaturation experiments indicated that the WT CBS protein is thermodynamically more stable than the R336C mutant, suggesting a destabilizing effect of the p.R336C mutation. • This study provides mechanistic insight into the pathogenicity of the p.R336C mutation that leads to a severe homocystinuria phenotype.