Molecular basis for the p phenotype - Identification of distinct and multiple mutations in the (alpha 1,4-galactosyltransferase gene in Swedish and Japanese individuals

p phenotype individuals lack both P-k (Gb3) and P (Gb4) glycolipid antigens of the P blood group system. To explore the molecular basis for this pheno type, DNA sequences of Gb3 synthase (alpha1,4-galactosyltransferase; alpha1 ,4Gal-T) in six p phenotype individuals from Japan and Sweden were analyzed . A missense mutation P251L and a nonsense mutation W261stop in three and o ne Japanese indivuiduals, respectively, and missense mutations M183K and G1 87D in one each of two Swedish p individuals were found, indicating that p individuals from Japan and Sweden have distinct and multiple homozygous poi nt mutations in the coding region. In the function analysis of the mutated alpha1,4Gal-Ts by the transfection of the expression vectors, P251L and M18 3K mutations showed complete loss of enzyme function, and W261stop and G187 D mutations resulted in the marginal activity. BLAST analysis of homologous sequences of alpha1,4Gal-T revealed that three residues, Met(183), Gly(187 ), and Pro(251), at which missense mutations were found, were highly conser ved among all species examined, suggesting their importance for the functio n of alpha1,4Gal-T.