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  • Title: Aberrant intracellular trafficking of a variant B glycosyltransferase.
    Author: Seltsam A, Grüger D, Just B, Figueiredo C, Gupta CD, Deluca DS, Blasczyk R.
    Journal: Transfusion; 2008 Sep; 48(9):1898-905. PubMed ID: 18513251.
    Abstract:
    BACKGROUND: Little is known about the mechanism by which amino acid polymorphisms outside the catalytically active cleft of ABO glycosyltransferases cause weak ABO phenotypes. STUDY DESIGN AND METHODS: Extensive ABO phenotyping and genotyping were performed to classify the blood of a healthy blood group O donor with weak isoagglutinins. ABO antigen and glycosyltransferase expression profiles were then studied in eukaryotic transfection experiments, and the topology of ABO glycosyltransferase was analyzed. RESULTS: The donor's red blood cells were retyped as A(weak), and his serum contained weakly reactive anti-A and anti-B. Sequence analysis revealed two novel ABO alleles. A donor splice-site mutation detected at the exon 6/intron 6 junction of an ABO*A101 allele was predicted to result in skipping exon 6 in the mRNA. The other haplotype displayed a single 688G>C substitution predicting a Gly230Arg exchange in the catalytic domain in an otherwise normal ABO*B101 allele. The transfection studies revealed very weak expression of B antigen by the novel ABO*B allele. According to the topologic analysis, steric hindrance due to the Gly230Arg exchange may cause conformational changes in the variant B transferase. Compared to the wild-type B transferase, the transfected cells exhibited lower-level protein expression and intracellular dislocation. CONCLUSION: This study provides first evidence that aberrant trafficking of variant ABO transferases may be involved in the formation of weak ABO phenotypes.
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