The A-type ATP synthase subunit K of Methanopyrus kandleri is deduced from its sequence to form a monomeric rotor comprising 13 hairpin domains.

The ntpK gene of the archaeon Methanopyrus kandleri encodes the equivalent of the c subunit of ATP synthase. The gene product contains 1021 residues and consists of 13 homologous domains, each one corresponding to a single helical hairpin. The amino acid sequence of the domains is highly conserved, ranging between 50 and 80% sequence identity. Each of the 13 domains contains a conserved Gln and Glu residue in the N- and C-terminal helix, respectively, both of which are believed to be involved in cation binding. The protein is likely to form the monomeric rotor of the ATP synthase that consists of 13 hairpin domains.