Missense mutations outside the catalytic domain of the ABO glycosyltransferase can cause weak blood group A and B phenotypes.
BACKGROUND
Only little is known about the impact of amino acid substitutions outside an enzyme's active site on A and B transferase activity.


METHODS
A panel of blood group A- and B-specific plasmids containing the six known missense mutations of the coding sequence upstream of exon 6 of the ABO gene were constructed. HeLa cells were used to transfect ABO expression plasmids.


RESULTS
Expression of ABO variants containing single or multiple missense mutations in HeLa cells resulted in a significant decrease in the percentage of antigen-expressing cells (up to 29%) and in mean fluorescence intensity (MFI; up to 50%) compared to transfection with ABO*A101 or ABO*B101. Coexpression of the respective antithetical wild-type construct (ABO*A101 and ABO*B101, respectively) further reduced cell surface expression of variant ABO constructs in regard to the percentage of expressing cells (up to 53% decrease) and MFI (up to 59% decrease).


CONCLUSIONS
Weak A and B subgroups can arise from transferases with amino acid changes in the N-terminal domain, particularly in AB phenotypes, where normal A1 or B1 glycosyltransferases compete for the same substrates.
Seltsam
Axel
A
Department of Transfusion Medicine, Hannover Medical School, Hannover, Germany.
Blasczyk
Rainer
R
D000017:ABO Blood-Group System / Q000276:immunology / Q000378:metabolism*; D000483:Alleles; D019943:Amino Acid Substitution; D003062:Codon / Q000235:genetics; D005091:Exons / Q000235:genetics; D005700:Galactosyltransferases / Q000737:chemistry / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008958:Models, Molecular; D020125:Mutation, Missense; D017350:N-Acetylgalactosaminyltransferases / Q000737:chemistry / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D010641:Phenotype; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000502:physiology; D014162:Transfection
D000017:ABO Blood-Group System; D003062:Codon; D011993:Recombinant Fusion Proteins; D005700:Galactosyltransferases; D017350:N-Acetylgalactosaminyltransferases; C003742:UDPgalactosamine-galactose acetylgalactosaminyltransferase; C023155:blood-group-substance alpha-D-galactosyltransferase