Structural basis for red cell phenotypic changes in newly identified, naturally occurring subgroup mutants of the human blood group B glycosyltransferase

Abstract

The genetic background for B(w) phenotypes is very heterogeneous but usually arises through seemingly random missense mutations throughout the last ABO exon. The targeted amino acid residues, however, are well conserved during evolution. Based on analysis of the resulting structural changes in the glycosyltransferase, the mutations are likely to disrupt molecular bonds of importance for enzymatic function.

Structures of Complexes of a Metal-independent Glycosyltransferase GT6 from Bacteroides ovatus with UDP-N-Acetylgalactosamine (UDP-GalNAc) and Its Hydrolysis Products

“…Previously, crystallographic and mutational studies of structure-function relationships have been conducted with the catalytic domains of mammalian metal-dependent GT6, bovine α3GT (17, 22–25), and human GTA/GTB (18, 26–28). In the complexes containing Mn 2+ and UDP or a UDP derivative, the metal interacts with the aspartates of the D X D motif (residues Asp 225 -Val-Asp 227 in α3GT), through a single interaction with Asp 225 and a bidentate interaction with Asp 227 , and also interacts with an oxygen from each of the α- and β-phosphates of the UDP (17, 18).…”

ABO, H, and Lewis Systems

“…Sera of B v individuals contain a form of anti -B; no GTB activity could be detected. Of 18 Hong Kong Chinese with B v red cells, 17 had a B allele containing 695T > C, Leu232Pro ( Bw11 [346] ) and one had a B allele containing 721C > T, Arg241Trp ( Bw03 [261] ); no mutation was detected in the coding region of the B gene of an AB v individual [351] . Of 18 Hong Kong Chinese with B v red cells, 17 had a B allele containing 695T > C, Leu232Pro ( Bw11 [346] ) and one had a B allele containing 721C > T, Arg241Trp ( Bw03 [261] ); no mutation was detected in the coding region of the B gene of an AB v individual [351] .…”

“…Numerous other ABO alleles responsible for variant B phenotypes have been described, mostly as B w [159,215,261,317,346] . A structural analysis, based on the crystal structure of GTB, demonstrated that the mutations in variant B alleles are likely to disrupt molecular bonds important for enzyme function [346] .…”

The p.R168Q mutation is associated with the Bw phenotype and a predicted decrease in the stability of the resulting ABO glycosyltransferase

“…Single‐nucleotide alteration in the ABO gene can affect the enzyme activity or protein quantity 1‐7. Several different techniques have been used to elucidate the mutation–function relationship of a mutant ABO glycosyltransferase (GT).…”

“…Several different techniques have been used to elucidate the mutation–function relationship of a mutant ABO glycosyltransferase (GT). The crystal X‐ray diffraction and three‐dimensional (3D) molecular modeling have described the conformation of the mutant enzyme 1‐4. Some in vitro expression studies have evaluated the expression level of ABO antigen on cell lines transfected with plasmids containing recombinant mutants, and flow cytometry analysis of red blood cells (RBCs) has been utilized to characterize different ABO subgroups .…”