Abstract: Objective The phenotype of 1,3-D-galactosyltransferase p.Arg187Cys mutation previously found in Chinese population is normal B type. This study aims to explore the possible molecular mechanism of AB subtype induced by this mutation. Methods We identified the blood group and serotype of a Chinese individual by immunoserology. The enhancer, promoter, all seven exons and flanking sequences of ABO gene were amplified by PCR, and the amplified products were sequenced. The 3D molecular model was constructed by chimera software to predict the effect of mutation on the structure of 1,3-D-galactosyltransferase. Results It was identified as ABx subtype by serological method. The ABO gene sequencing showed that this healthy individual was A1.02/B.03 genotype; Only c.559C>T（p.Arg187Cys）mutation was detected in exon 7 of allele B, and no mutation was found in the rest of ABO gene. The 3D molecular model analysis showed that p.Arg187Cys mutation changed the local hydrogen bonding network of 1,3-D-galactosyltransferase, which may decrease enzyme activity. When co-expressed with A gene, it showed weak B phen-otype under the competition of 1,3-N-acetylgalactosamine transferase. Conclusion The c.559C>T mutation of ABO*B gene leads to the formation of ABx subtype by weakening the activity of 1,3-D-galactosyltransferase and the competition of ABO*A gene products.

Key words: ABO blood group, Abx subgroup, Sequence analysis, 3D molecular model