ABO blood group A transferase and its codon 69 substitution enzymes synthesize FORS1 antigen of FORS blood group system

Abstract

Human histo-blood group A transferase (AT) catalyzes the biosynthesis of oligosaccharide A antigen important in blood transfusion and cell/tissue/organ transplantation. This enzyme may synthesize Forssman antigen (FORS1) of the FORS blood group system when exon 3 or 4 of the AT mRNA is deleted and/or the LeuGlyGly tripeptide at codons 266–268 of AT is replaced by GlyGlyAla. The Met69Ser/Thr substitutions also confer weak Forssman glycolipid synthase (FS) activity. In this study, we prepared the human AT derivative constructs containing any of the 20 amino acids at codon 69 with and without the GlyGlyAla substitution, transfected DNA to newly generated COS1(B3GALNT1 + A4GALT) cells expressing an enhanced level of globoside (Gb4), the FS acceptor substrate, and immunologically examined the FORS1 expression. Our results showed that all those substitution constructs at codon 69 exhibited FS activity. The combination with GlyGlyAla significantly increased the activity. The conserved methionine residue in the ABO , but not GBGT1 , gene-encoded proteins may implicate its contribution to the separation of these genes in genetic evolution. Surprisingly, with increased Gb4 availability, the original human AT with the methionine residue at codon 69 was also demonstrated to synthesize FORS1, providing another molecular mechanism of FORS1 appearance in cancer of ordinary FORS1-negative individuals.

Mixed‐Up Sugars: Glycosyltransferase Cross‐Reactivity in Cancerous Tissues and Their Therapeutic Targeting

“…Following this discovery, site-directed mutagenesis was used to determine which amino acids at codon 69 could also provide AT with FS activity, in addition to serine and threonine. [63] It was determined that many amino acids could promote this enzymatic promiscuity. In more detail, methionine is conserved in the ABO genes but not in the GBGT1 gene in the codons corresponding to codon 69 of AT, supporting the idea that it had helped establish the separation between the enzymatic activities of the two enzymes.…”

“…Following this discovery, site‐directed mutagenesis was used to determine which amino acids at codon 69 could also provide AT with FS activity, in addition to serine and threonine [63] . It was determined that many amino acids could promote this enzymatic promiscuity.…”

“…Substrate availability is of crucial importance when it comes to enzyme activity, as we mentioned earlier. In that work, [63] improved concentrations of globoside were achieved by stable expression of globoside synthase encoded by B3GALNT1 and Gb3/CD77 synthase (P1/P k synthase, lactosylceramide α1,4‐galactosyltransferase) encoded by A4GALT. When these two enzymes were present, FORS1 antigen production was detected even with wild‐type AT (methionine at codon 69).…”

May the FORS be with you: a system sequel

“…16,17 The effect of different substitutions and/or deletions in the ABO and GBGT1 genes derived from both humans and FORS system update mice has been tested and evaluated in a series of articles by Yamamoto and colleagues. [18][19][20][21] The aim has been to provide more insight into the specificity of glycosyltransferases included in the GT6 family and how the specificity of one can be changed to the other's in an experimental setting.…”

Role of Antigen Determinants a and B of AB0 Blood Group System in Human Disease Development (Mini Review)

“…AB0 system antigens chemical structure is presented with molecules of glycoproteins fi xed on erythrocyte cytoplasmic membrane surface. The difference between blood group antigens consists in different terminal oligosaccharide chain glycans [1,2]. Antigens of AB0 system are presented not only on erythrocyte membrane surface, but also in secretory epithelium of salivary glands, gastrointestinal organs, sex glands and respiratory system.…”