RESUMEN
BACKGROUND: Weak blood group A and B phenotypes are correlated with ABO glycosyltransferases exhibiting single-amino-acid changes and/or C-terminal modifications. STUDY DESIGN AND METHODS: A healthy donor diagnosed as having weak A antigen expression and his two children were subjected to extensive ABO typing. HeLa cells were used to transfect ABO expression plasmids. RESULTS: The donor's red blood cells were type A(weak)B and his serum sample contained weakly reactive anti-A(1) antibodies. A single T>C transition identified at the +2 position of the start codon of an ABO*A101 allele predicted the disruption of this methionine codon. In the transfection studies, a significant reduction of A activity was observed on HeLa cells transfected with a plasmid containing the variant ABO*A allele. Coexpression of the respective antithetical ABO*B101 wild-type construct further reduced cell surface A antigen expression. Similar expression results were obtained with ABO constructs in which the Met(1) start codon and five alternative start sites at codons 20, 26, 43, 53, and 69 had successively been interrupted. CONCLUSION: The donor's weak blood group A phenotype most likely resulted from expression of an N-truncated A transferase triggered by alternative translation start sites in the transmembrane domain or stem region.
Asunto(s)
Sistema del Grupo Sanguíneo ABO/genética , Alelos , Codón Iniciador/genética , Glicosiltransferasas/genética , Mutación Puntual , Biosíntesis de Proteínas/genética , Tipificación y Pruebas Cruzadas Sanguíneas/métodos , Femenino , Expresión Génica , Células HeLa , Humanos , Masculino , Linaje , Fenotipo , Plásmidos , Procesamiento Proteico-Postraduccional/genética , Estructura Terciaria de Proteína , Transfección/métodosRESUMEN
BACKGROUND: Owing to a single-base deletion, the vast majority of ABO*O alleles encode for a truncated and catalytically inactive ABO glycosyltransferase, leading to the generation of a premature stop codon. Less frequent nondeletional ABO*O alleles such as ABO*O03, in contrast, have nonsynonymous mutations that may abolish the protein's enzyme activity by altering its sugar-binding site. STUDY DESIGN AND METHODS: Extensive ABO phenotyping and genotyping were performed in healthy blood group O donors with weak anti-A isoagglutinins and their relatives as well as in blood group O donors selected for the presence of ABO*O03. HeLa cells were used to transfect ABO expression plasmids. RESULTS: Donors or relatives carrying ABO*O03 and/or its rare variant ABO*Aw08 in homozygous (n = 2) or heterozygous (n = 14) form showed weak A antigen expression detectable only by adsorption-elution (n = 15) or by monoclonal anti-A typing (n = 1). The serum samples of most donors (n = 13) contained weak anti-A; in the remaining donors, anti-A isoagglutinin reactivity was in the normal range. In the transfection studies, weak A antigen expression on HeLa cells transfected with plasmids containing ABO*O03 or ABO*Aw08 expression constructs was detectable only by adsorption-elution. CONCLUSION: The data provide evidence that nondeletional ABO*O03-like alleles produce detectable amounts of A antigens.