Fig. 2. CATP-1 encodes a cation-transporting ATPase of the P-type family with an ATPase-independent activity. (A) Phylogenetic tree of C. elegans and vertebrate Ca²⁺-, H⁺/K⁺- and Na⁺/K⁺-ATPases determined using the ClustalW analysis on full-length sequences. SCA-1, PMR-1, EAT-6, C01G12.8, CATP-1, C02E7.1 and C09H5.2 are C. elegans proteins. (B) Domain structure of human Na⁺/K⁺ P-type ATPase 1 and CATP-1. TM, transmembrane domain (black); P, phosphorylable P-domain (light gray); N, ATP-binding N-domain (dark gray). (C-E) CATP-1 has an ATPase-independent activity. (C,D) Amino-acid sequence comparison among the predicted H⁺/K⁺ (HK) and Na⁺/K⁺ (NK) P-type ATPase subunits. The amino-acid numbers are according to C. elegans CATP-1. Residues identical or similar in more than 50% of the proteins are shaded in black or gray, respectively; residues similar to the identity consensus are also shaded in gray (BOXSHADE 3.21, http://www.ch.embnet.org/software/BOX_form.html). (C) Part 1 of the phosphorylable P-domain. Arrow indicates the phosphorylable aspartate characteristic of P-type ATPases. (D) ATP-binding region of the N-domain. Arrow indicates the arginine equivalent to R544 in pig kidney Na⁺/K⁺-ATPase, which is essential for ATP binding (Jacobsen et al., 2002). (E) Survival on 0.75 mM DMPP. The D409E mutation disrupts the obligatory phosphorylation site conserved in all P-type ATPases. Error bars represent s.e.m. (n3 independent experiments, N81 individuals, two independent lines). Two pump-dead mutants of CATP-1 partially rescue catp-1(kr17) DMPP resistance (^*P<0.05, Mann-Whitney test).