Functional assays testing pathogenicity of 14 cystathionine-beta synthase mutations

Area of Science:

• Biochemistry
• Genetics
• Enzyme kinetics

Background:

• Homocystinuria is a genetic disorder often caused by mutations in the cystathionine beta-synthase (CBS) gene.
• Understanding the functional impact of CBS mutations is crucial for diagnosing and managing homocystinuria.

Purpose of the Study:

• To characterize the enzymatic activity and protein stability of 14 different CBS mutations found in homocystinuric patients.
• To correlate genotype with observed biochemical phenotypes.

Main Methods:

• Heterologous expression of 14 mutant CBS alleles in E. coli.
• In vitro enzyme activity assays.
• Western blot analysis on denaturing and non-denaturing polyacrylamide gels to assess protein levels and quaternary structure.

Main Results:

• Eleven out of 14 CBS mutations resulted in enzyme activity below 4% of wild-type.
• Mutations p.A226T, p.M173V, and p.R548Q retained 20%, 40%, and 60% of wild-type activity, respectively.
• Most mutants showed reduced protein levels and impaired quaternary structure formation, with p.R548Q exhibiting partial retention of structure.

Conclusions:

• The majority of characterized CBS mutations severely impair enzyme function and protein stability.
• The variant p.R548Q represents a rare case with relatively preserved activity and structural integrity, suggesting a distinct clinical or biochemical profile.