A comparison of the mutation spectra of Menkes disease and Wilson disease

Abstract

The genes for two copper-transporting ATPases, ATP7A and ATP7B, are defective in the heritable disorders of copper imbalance, Menkes disease (MNK) and Wilson disease (WND), respectively. A comparison of the two proteins shows extensive conservation in the signature domains, with amino acid identities outside of the conserved domains being limited. The mutation spectra of MNK and WND were compared to confirm and refine further regions critical for normal function. Mutations were found to be relatively widespread; however, the majority was concentrated within defined functional domains and membrane-spanning segments, reinforcing the importance of these regions for protein function. Of the total published point mutations in ATP7A, 23.0% are splice-site, 20.7% nonsense, 17.2% missense, and 39.1% small insertions/deletions. There is a high prevalence (58.2%) of missense mutations in ATP7B. For the other mutations in ATP7B, 7.4% are splice-site, 7.4% nonsense, and 27.0% small insertions/deletions. A region of possible importance is the intervening sequence between the last copper-binding domain and the first transmembrane helix, as this region has a high percentage of MNK mutations. Similarly, the region containing the ATP-binding domain has 24.6% of all WND mutations. The study of mutation locations is useful for defining critical regions or residues and for efficient molecular diagnosis.

Twenty-four novel mutations in Wilson disease patients of predominantly European ancestry

“…Two of these lie within transmembrane (Tm) domains 2 and 5, with scores of 0.21,and 0.07 respectively, and we consider them to be disease causing because of their positions within ATP7B. Changes in the copper 6 to Tm1 region have been found in ATP7A (Hsi and Cox, 2004) and may alter flexibility of the protein in this region, although SIFT scores for two mutations are 0.21 and 0.08. Mutations are not expected between copper binding domains 5 and 6 (p.Y532H) or within copper 6 (p.G591D), because of the redundancy of copper domains and the lack of mutations in ATP7A in this region (Hsi and Cox, 2004).…”

“…Changes in the copper 6 to Tm1 region have been found in ATP7A (Hsi and Cox, 2004) and may alter flexibility of the protein in this region, although SIFT scores for two mutations are 0.21 and 0.08. Mutations are not expected between copper binding domains 5 and 6 (p.Y532H) or within copper 6 (p.G591D), because of the redundancy of copper domains and the lack of mutations in ATP7A in this region (Hsi and Cox, 2004). The change in hydrophobicity and replacement by histidine, a residue typically involved in copper binding (p.Y532H) and a SIFT score of 0 (p.G591D), make them acceptable as disease causing.…”

Crystallization and preliminary X-ray studies of the N-domain of the Wilson disease associated protein

“…The long loop comprising residues 1114-1142 is not involved in ATP binding (Dmitriev et al, 2006) and there are no known Wilson's disease mutations in this region (Hsi & Cox, 2004), which implies that this region is not critical for enzyme function and that the core N-domain structure would not be altered by deletion of this loop. At the same time, the disordered state of this loop may have prevented successful crystallization of the full-length N-domain.…”

Identification of the Transmembrane Metal Binding Site in Cu+-transporting PIB-type ATPases

“…For instance, mutations of the human Cu ϩ -ATPases, ATP7A and ATP7B, leads to Menkes' and Wilson's disease, respectively (1,2). Similarly, the knockout of Arabidopsis thaliana Cu ϩ -ATPase genes produces significant, and in some cases lethal, physiological alterations (3,4).…”

“…Biochemical studies supporting different aspects of this cycle have shown metal-dependent ATPase activity, metal transport capability, interaction of ATP with high and low affinity, phosphorylation of the invariant Asp in the DKTGT sequence, distinct E1P and E2P forms, and the typical inhibition by vanadate observed in all P-type ATPases (6, 10 -16). Cu ϩ -ATPases have eight transmembrane segments (TMs) 1 with a large cytoplasmic loop located between their sixth (H6) and seventh (H7) TMs and responsible for ATP hydrolysis (8,9,17,18) (Fig. 2).…”