p.R180C mutation of glycosyltransferase B leads to B subgroup, an in vitro and in silico study.

Background And Objectives: Dysfunctional glycosyltransferase A or B may lead to incomplete glycosylation of H antigen and atypical ABO blood group with weak A or B phenotypes, posing challenges for blood typing for transfusion.

Materials And Methods: Serological studies and ABO gene analysis were performed. Flow cytometry was performed on HeLa cells transfected glycosyltransferase B expressing plasmids. Agglutination of transfected cells and total glycosyltransferase B transfer capacity were examined. Molecular dynamics simulations were used to explore possible dynamic conformational changes around the binding pocket.

Results: We identified a mutation c.538C>T (p. R180C) of B allele in a Chinese donor and his father with AB phenotype. In vitro expression study showed that mutation p.R180C, although not affecting expression of glycosyltransferase B, impaired H to B antigen conversion. The in silico analyses found that the residue Arg180 on the internal loop next to the entry of the binding pocket may have its long side chain salt-bridged with the highly flexible C-terminal carboxyl and contribute to the catalysis of H to B antigen conversion.

Conclusion: The p.R180C mutation impairs the conversion from H to B antigen and leads to weak B phenotype. Dynamic interaction between Arg180 and C-terminal of glycosyltransferase B may stabilize its binding with UDP-galactose and facilitate H/B antigen conversion.