Characterization of wild-type and mutants of recombinant human GTP cyclohydrolase I: relationship to etiology of dopa-responsive dystonia.
To explore the molecular etiology of two disorders caused by a defect in GTP cyclohydrolase I--hereditary progressive dystonia with marked diurnal fluctuation (HPD), also known as dopa-responsive dystonia (DRD), and autosomal recessive GTP cyclohydrolase I deficiency--we purified and analyzed recombinant human wild-type and mutant GTP cyclohydrolase I proteins expressed in Escherichia coli. Mutant proteins showed very low enzyme activities, and some mutants were eluted at a delayed volume on gel filtration compared with the recombinant wild-type. Next, we examined the GTP cyclohydrolase I protein amount by western blot analysis in phytohemagglutinin-stimulated mononuclear blood cells from HPD/DRD patients. We found a great reduction in the amount of the enzyme protein not only in one patient who had a frameshift mutation, but also in an HPD/DRD patient who had a missense mutation. These results suggest that a dominant-negative effect of chimeric protein composed of wild-type and mutant subunits is unlikely as a cause of the reduced enzyme activity in HPD/DRD patients. We suggest that reduction of the amount of the enzyme protein, which is independent of the mutation type, could be a reason for the dominant inheritance in HPD/DRD.
Suzuki
T
T
Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Aichi, Japan.
Ohye
T
T
Inagaki
H
H
Nagatsu
T
T
Ichinose
H
H
D000595:Amino Acid Sequence; D001708:Biopterins / Q000031:analogs & derivatives / Q000378:metabolism; D004252:DNA Mutational Analysis; D020821:Dystonic Disorders / Q000201:enzymology / Q000235:genetics*; D016368:Frameshift Mutation; D006136:GTP Cyclohydrolase / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D005799:Genes, Dominant; D005808:Genes, Recessive; D006801:Humans; D008969:Molecular Sequence Data; D009447:Neuroblastoma / Q000473:pathology; D010649:Phenylalanine / Q000097:blood; D017354:Point Mutation; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured
D011993:Recombinant Fusion Proteins; D001708:Biopterins; D010649:Phenylalanine; D006136:GTP Cyclohydrolase; C003402:sapropterin