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#ABO blood group

2 public questions tagged with this topic.

Glycolipid and Phospholipid

Which of the following enzymes is responsible for converting H antigen to A antigen?

Epitope conversion H to A illustrates exquisite donor acceptor specificity retaining glycosyltransferases Golgi apparatus. H antigen acceptor Gal beta1-4(Fuc alpha1-2)GlcNAc presents free three hydroxyl galactose for extension. A transferase GTA encoded chromosome nine q34 binds UDP GalNAc donor coordinated DxD motif manganese induced fit where Leu two sixty six Met and Gly two sixty eight Ala differentiate GalNAc versus galactose specificity compared B enzyme GTB. Catalysis forms alpha one three linkage adding GalNAc completing A antigen GalNAc alpha1-3(Fuc alpha1-2)Gal responsible ABO type A serology. B transferase analogous adds Gal forming B antigen distinct. Fucosyltransferase FUT1 builds H earlier adding fucose alpha one two forming H substance, glycosidase hydrolyzes glycosidic bonds removing rather adding sugars opposite reaction catabolic. Expression in erythroid precursors via GATA1 transcription factor, secretor regulated FUT2 fucosyltransferase in epithelia. Single amino acid changes swap A B activity demonstrating evolution blood groups from single ancestral gene duplication divergence. Reaction paradigmatic glycobiology provides molecular basis forensic blood typing organ transplantation compatibility immunology examination questions about carbohydrate antigens and enzyme specificity and allelic variation.

Ref: Letts et al., J Biol Chem 2006, Crystal structure ABO transferases GalNAc transferase mechanism H to A.

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Glycolipid and Phospholipid

Which statement is true about ABO blood group antigens?

ABO antigens represent terminal glycosylation differences on H precursor anchored glycolipid or glycoprotein paragloboside type two chain precursor. H synthesis requires FUT1 alpha one two fucosyltransferase attaching fucose galactose beta1-4 GlcNAc forming Fuc alpha1-2 Gal structure. Functional A allele encodes alpha one three N acetylgalactosaminyltransferase GTA adding GalNAc galactose H forming A trisaccharide GalNAc alpha1-3(Fuc alpha1-2)Gal antigen A. B allele encodes alpha one three galactosyltransferase GTB adding galactose forming B trisaccharide Gal alpha1-3(Fuc alpha1-2)Gal antigen B. O allele harbors two six one delG frameshift producing truncated soluble inactive enzyme lacking catalytic domain so H remains unconverted due absent transferase activity producing O phenotype H antigen only. O individuals therefore lack A B glycosyltransferases but retain FUT1 FUT2 fucosyltransferases required Bombay phenotype hh. Misstatements Type A adding galactose or Type B lacking modification incorrect. Genetics explains transfusion reactions anti A anti B IgM natural antibodies isoagglutinins and Bombay phenotype hh lacking fucosyltransferase producing no H substrate requiring Bombay blood donations extremely rare compatible blood type cases.

Ref: Yamamoto F., Transfusion Med Rev 2004, ABO genetics O inactivity transferase and H antigen.

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