Phenotypic variation among seven members of one family with deficiency of hypoxanthine-guanine phosphoribosyltransferase.
We describe a family of seven boys affected by Lesch-Nyhan disease with various phenotypes. Further investigations revealed a mutation c.203T>C in the gene encoding HGprt of all members, with substitution of leucine to proline at residue 68 (p.Leu68Pro). Thus patients from this family display a wide variety of symptoms although sharing the same mutation. Mutant HGprt enzyme was prepared by site-directed mutagenesis and the kinetics of the enzyme revealed that the catalytic activity of the mutant was reduced, in association with marked reductions in the affinity towards phosphoribosylpyrophosphate (PRPP). Its Km for PRPP was increased 215-fold with hypoxanthine as substrate and 40-fold with guanine as substrate with associated reduced catalytic potential. Molecular modeling confirmed that the most prominent defect was the dramatically reduced affinity towards PRPP. Our studies suggest that the p.Leu68Pro mutation has a strong impact on PRPP binding and on stability of the active conformation. This suggests that factors other than HGprt activity per se may influence the phenotype of Lesch-Nyhan patients.
Department of Metabolic Biochemistry, Hôpital Necker-Enfants Malades, AP-HP, 149 rue de Sèvres, 75015 Paris, France; School of Medicine, Paris Descartes University Sorbonne Paris Cité, 15 rue de l'Ecole de Médecine, 75006 Paris, France. Electronic address: irene.ceballos@nck.aphp.fr.
Irène
I
Ceballos-Picot
Franck
F
Augé
Rong
R
Fu
Anne
A
Olivier-Bandini
Julie
J
Cahu
Brigitte
B
Chabrol
Bernard
B
Aral
Bérengère
B
de Martinville
Jean-Paul
JP
Lecain
H A
HA
Jinnah
D000293:Adolescent; D000328:Adult; D019943:Amino Acid Substitution; D002648:Child; D003062:Codon; D004789:Enzyme Activation; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics*; D007700:Kinetics; D007926:Lesch-Nyhan Syndrome / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D008958:Models, Molecular; D009154:Mutation; D010375:Pedigree; D010641:Phenotype; D011485:Protein Binding; D011487:Protein Conformation; D055550:Protein Stability; D055815:Young Adult
D003062:Codon; D007041:Hypoxanthine Phosphoribosyltransferase
HGprt; Lesch–Nyhan disease; Molecular modeling; PRPP; Phenotype–genotype; Variants