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J. Biol. Chem., Vol. 276, Issue 18, 15225-15231, May 4, 2001
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From the Hereditary tyrosinemia type 1 (HT1) is an
autosomal recessive disease caused by a deficiency of the enzyme
involved in the last step of tyrosine degradation, fumarylacetoacetate
hydrolase (FAH). Thus far, 34 mutations in the FAH gene have been
reported in various HT1 patients. Site-directed mutagenesis of the FAH cDNA was used to investigate the effects of eight missense
mutations found in HTI patients on the structure and activity of FAH.
Mutated FAH proteins were expressed in Escherichia coli and
in mammalian CV-1 cells. Mutations N16I, F62C, A134D, C193R, D233V, and
W234G lead to enzymatically inactive FAH proteins. Two mutations
(R341W, associated with the pseudo-deficiency phenotype, and Q279R)
produced proteins with a level of activity comparable to the wild-type enzyme. The N16I, F62C, C193R, and W234G variants were enriched in an
insoluble cellular fraction, suggesting that these amino acid
substitutions interfere with the proper folding of the enzyme. Based on
the tertiary structure of FAH, on circular dichroism data, and on
solubility measurements, we propose that the studied missense mutations
cause three types of structural effects on the enzyme: 1) gross
structural perturbations, 2) limited conformational changes in the
active site, and 3) conformational modifications with no significant
effect on enzymatic activity.
Structural and Functional Analysis of Missense Mutations in
Fumarylacetoacetate Hydrolase, the Gene Deficient in Hereditary
Tyrosinemia Type 1*
,
,
¶
Laboratory of Cell and Developmental
Genetics, Department of Medicine, Pavillon C.-E. Marchand,
Université Laval, Ste-Foy, Québec G1K 7P4, Canada and the
§ Department of Biochemistry and Molecular Biology, Indiana
University School of Medicine, Indianapolis, Indiana 46202
*
This work was supported by Medical Research Council of
Canada (now Canadian Institute of Health Research) Grant
MT-11081 (to R. M. T.) and a National Institutes of Health
grant (to D. E. T.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
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