Altered coding for a strictly conserved di-glycine in the major bilirubin UDP-glucuronosyltransferase of a Crigler-Najjar type I patient.

摘要: Abstract The characterization (Ritter, J. K., Chen, F., Sheen, Y. Y., Tran, H. M., Kimura, S., Yeatman, M. T., and Owens, I. S. (1992) Biol. Chem. 267, 3257-3261) of the single-copy UGT1 gene complex locus encoding both bilirubin phenol UDP-glucuronosyltransferases (transferase) has been critical to determination genetic defects in Crigler-Najjar patients. (UGT1A-UGT1M) codes for at least two bilirubin, three bilirubin-like, eight transferase isozymes. In 5′ region, a minimum 13 different exons 1, each with an upstream promoter, are arrayed series 4 common 3′ region locus. Each exon 1 encodes amino terminus transferase, encode carboxyl isoform. Although deleterious mutation inactivates entire locus, as we report here UGT1A Type I patient, affects that single Recessively inherited mutant alleles predominant isozyme, HUG-Br1 protein, substituted Arg Gly codon 276 (G276R) abolishing conserved di-glycine. HUG-Br1-G276R protein expressed COS-1 cells had no detectable glucuronidating activity either pH 7.6 or 6.4. bilirubin-type isozymes contains peptide between residues 270 288, all contain di-glycine approximately position 276-277, making it strictly conserved. Structure-function relationship was studied by site-directed mutations cDNA; G276A, G276Q, G276E, G276I, P270G mutants were inactive, V275I- P285G-altered transferases normal activity. Conservation related baculoviral ecdysone UDP-glucosyltransferase confirms role Gly-276 well other residues.