Evaluation of amino acid substitution p. Asp183Gly of A‐glycosyltransferase enzyme in an individual with the A weak B phenotype

Background Amino acid substitutions resulting from variants in the ABO gene are often found to impact glycosyltransferase function, leading to incomplete glycosylation of the H antigen and the emergence of ABO subgroups with weak A or B phenotypes. Here, we identify a novel ABO*AW allele and investigate the underlying mechanism. Study Design and Methods RBCs were phenotyped by standard serology methods. The full coding region of the ABO gene, as well as its proximal promoter region, splice sites and the erythroid cell‐specific regulatory elements in intron 1 were sequenced. The haplotype of the variant allele was analyzed through cloning sequencing. The effect of the c.548A>G variant was evaluated using a three‐dimensional model generated with PyMOL software, and the free energy change (ΔΔG) was calculated by SNPeffect. Results Serological analysis detected the A weak B phenotype in the subject, and gene sequencing identified a variant c.548A>G (p.Asp183Gly) on the ABO*A1.02 backbone, resulting in an AW‐var / B.01 genotype. In silico analysis suggested that the p.Asp183Gly variant on the A allele may reduce the stability of A‐glycosyltransferase (GTA), as indicated by the ΔΔG values and a weakened hydrogen bond network in local conformation; thus, it may result in decreased enzyme activity and impair the catalysis of H to A antigen conversion. Conclusion A novel ABO allele ABO*A1.02 ( 548G ) was identified in an A weak B individual and computational evaluation indicated that residue Asp183 was a critical site for enzyme stability and efficacy, which is consistent with the altered phenotype encoded by alleles ABO*BW.04 (c.548A>G, p.Asp183Gly) and ABO*B3.06 (c.547G>A, p.Asp183Asn).