Aberrant intracellular trafficking of a variant B glycosyltransferase.
BACKGROUND
Little is known about the mechanism by which amino acid polymorphisms outside the catalytically active cleft of ABO glycosyltransferases cause weak ABO phenotypes.


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.


CONCLUSIONS
This study provides first evidence that aberrant trafficking of variant ABO transferases may be involved in the formation of weak ABO phenotypes.
Institute for Transfusion Medicine, Hannover Medical School, Hannover; the German Red Cross, Center for Transfusion Medicine Hagen, Hagen; and Biotest AG, Dreieich, Germany.
Axel
A
Seltsam
Daniela
D
Grüger
Burkhard
B
Just
Constança
C
Figueiredo
Christa Das
CD
Gupta
David S
DS
Deluca
Rainer
R
Blasczyk
D000017:ABO Blood-Group System / Q000235:genetics / Q000276:immunology; D000483:Alleles; D045744:Cell Line, Tumor; D005434:Flow Cytometry; D005838:Genotype; D016695:Glycosyltransferases / Q000235:genetics* / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009154:Mutation; D011110:Polymorphism, Genetic; D021381:Protein Transport; D014162:Transfection
D000017:ABO Blood-Group System; D016695:Glycosyltransferases