Functional characterization of missense mutations in ATP7B: Wilson disease mutation or normal variant?
Wilson disease is an autosomal recessive disorder of copper transport that causes hepatic and/or neurological disease resulting from copper accumulation in the liver and brain. The protein defective in this disorder is a putative copper-transporting P-type ATPase, ATP7B. More than 100 mutations have been identified in the ATP7B gene of patients with Wilson disease. To determine the effect of Wilson disease missense mutations on ATP7B function, we have developed a yeast complementation assay based on the ability of ATP7B to complement the high-affinity iron-uptake deficiency of the yeast mutant ccc2. We characterized missense mutations found in the predicted membrane-spanning segments of ATP7B. Ten mutations have been made in the ATP7B cDNA by site-directed mutagenesis: five Wilson disease missense mutations, two mutations originally classified as possible disease-causing mutations, two putative ATP7B normal variants, and mutation of the cysteine-proline-cysteine (CPC) motif conserved in heavy-metal-transporting P-type ATPases. All seven putative Wilson disease mutants tested were able to at least partially complement ccc2 mutant yeast, indicating that they retain some ability to transport copper. One mutation was a temperature-sensitive mutation that was able to complement ccc2 mutant yeast at 30 degreesC but was unable to complement at 37 degreesC. Mutation of the CPC motif resulted in a nonfunctional protein, which demonstrates that this motif is essential for copper transport by ATP7B. Of the two putative ATP7B normal variants tested, one resulted in a nonfunctional protein, which suggests that it is a disease-causing mutation.
Forbes
J R
JR
Department of Medical Genetics, 8-39 Medical Sciences Building, University of Alberta, Edmonton, Canada.
Cox
D W
DW
D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D001051:Apoenzymes / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D027682:Cation Transport Proteins; D002455:Cell Division; D002570:Ceruloplasmin / Q000378:metabolism; D003300:Copper / Q000378:metabolism; D000079922:Copper Transport Proteins; D000073840:Copper-Transporting ATPases; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics; D005816:Genetic Complementation Test; D006527:Hepatolenticular Degeneration / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007106:Immune Sera; D007501:Iron / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D010641:Phenotype; D011993:Recombinant Fusion Proteins / Q000276:immunology; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D013696:Temperature
D001051:Apoenzymes; C092974:CCC2 protein, S cerevisiae; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D000079922:Copper Transport Proteins; D018076:DNA, Complementary; D005656:Fungal Proteins; D007106:Immune Sera; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D003300:Copper; D007501:Iron; D002570:Ceruloplasmin; C085513:FET3 protein, S cerevisiae; D000251:Adenosine Triphosphatases; C000612464:ATP7B protein, human; D000073840:Copper-Transporting ATPases; D003545:Cysteine