The predicted secondary structures of the nucleotide‐binding sites of six cation‐transporting ATPases lead to a probable tertiary fold

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Abstract
Six cation‐dependent transporting ATPases have homologous sequences in the region assigned by chemical labelling to nucleotide binding. Comparison of the most highly conserved segments with other nucleotide‐binding domains showed that the sequences were consistent with a mononucleotide‐binding fold and enabled a number of likely folding topologies to be limited to two or three alternatives. One of these possible folds was topologically equivalent to adenylate kinase; this was taken as a model in which the significance of conserved amino acids was investigated. In this model conserved amino acids were grouped around a postulated ATP‐binding cleft, satisfactorily accounting for their degree of conservation.