Characterization of two missense mutations in human galactose-1-phosphate uridyltransferase: different molecular mechanisms for galactosemia.
We report the molecular characterization of two novel galactosemia mutations that exhibit different molecular phenotypes. Both are of the missense type with low or no residual enzyme activity. The R148W mutation results in an unstable protein, although messenger RNA is still produced. In contrast, the L195P mutation produces stable but inactive immunoreactive protein. The R148W mutation alters an amino acid that is not evolutionarily conserved, while the L195P mutation affects a well-conserved residue nine amino acids down-stream from the putative active site nucleophile. These mutations provide evidence that different mechanisms can result in galactosemia: destabilizing mutations in any given area of the protein and missense mutations in conserved domains of the enzyme resulting in low or no activity. These two mutant alleles represent the fifth and sixth galactosemia mutations and confirm the hypothesis that galactosemia results from a multiplicity of mutations at the molecular level.
Howard Hughes Medical Institute, Department of Cell Biology, Baylor College of Medicine, Texas Medical Center, Houston 77030-3498.
J K
JK
Reichardt
J W
JW
Belmont
H L
HL
Levy
S L
SL
Woo
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D003001:Cloning, Molecular; D005260:Female; D005693:Galactosemias / Q000201:enzymology / Q000235:genetics*; D005787:Gene Frequency; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D009838:Oligodeoxyribonucleotides; D010375:Pedigree; D011401:Promoter Regions, Genetic; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D011994:Recombinant Proteins / Q000378:metabolism; D005694:UTP-Hexose-1-Phosphate Uridylyltransferase / Q000235:genetics* / Q000378:metabolism
D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D012313:RNA; D005694:UTP-Hexose-1-Phosphate Uridylyltransferase