Sunday, 18 November 2007

My project (4)

…ATP 7B…


Gene map locus 13q14.3-q21.1
The ATP7B gene encodes a polypeptide that acts as a membrane copper-transport protein.
On YACs from the 13q14.3 region, Bull et al. (1993) identified a sequence similar to that coding for the proposed copper-binding regions of the putative ATPase gene defective in Menkes disease (MNK; 309400). They showed that this sequence forms part of a P-type ATPase gene that is very similar to MNK, with 6 putative metal-binding regions similar to those found in prokaryotic heavy metal transporters. The gene, designated ATP7B, is expressed in liver and kidney, and was found to lie within a 300-kb region likely to include the Wilson disease locus (WND). The identity between MNK and the newly identified ATP7B gene was 78% in the transduction region, 89% in the channel/phosphorylation regions, and 79% in the ATP-binding region. The predicted length of the gene product was 1,411 amino acids for ATP7B compared with 1,500 amino acids for MNK. The overall identity between the two was 57%.
Tanzi et al. (1993) used consensus DNA sequences for heavy metal binding motifs to identify homologous cDNA clones. One of these was mapped by PCR amplification and Southern blotting to contiguous YAC and cosmid clones that span the WND locus at chromosome 13q14.3. The cDNA detected a 7.5-kb RNA transcript expressed most strongly in liver and brain. Sequence analysis indicated several membrane-spanning domains, an ATPase consensus sequence, a hinge domain, a phosphorylation site, and at least 2 putative copper-binding sites. The deduced protein showed 62% amino acid homology to the Menkes disease gene.
Yang et al. (1997) stated that the full-length ATP7B protein contains 1,465 amino acids. They cloned a splice variant of ATP7B lacking exons 6, 7, 8, and 12 from a human brain cDNA library. The deduced protein contains 1,258 amino acids. Immunofluorescence localization and fractionation of a hepatoma cell line revealed that the full-length protein was associated with the Golgi apparatus and the shorter isoform was cytosolic. Full-length ATP7B did not redistribute in response to elevated copper levels, and it did not associate with the plasma membrane.

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