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.

STUDY DESIGN AND 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 ABOA101 or ABOB101. Coexpression of the respective antithetical wild-type construct (ABOA101 and ABOB101, 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).

CONCLUSION

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.