Primary structural constraints of P-loop of mitochondrial F1-ATPase from yeast

Nucleotide binding proteins, including ras, elongation factor Tu, adenylate kinase, and the mitochondrial F1-ATPase have a glycine-rich motif known as the P-loop or the Walker A sequence (Walker, J. E., Saraste, M., Runswick, M. J., and Gay, N. J. (1982) EMBO J. 1, 945-951). The primary structural constraints have been determined in the P-loop located in the beta-subunit of the mitochondrial ATPase from yeast. The primary structural constraints were determined for 9 residues that form the P-loop, 190Gly-Gly-Ala-Gly-Val-Gly-Lys-Thr-Val198. Each residue was tested individually for possible functional replacements while keeping the primary structure of the remainder of the molecule constant. This analysis indicates with greater than 95% confidence that Gly190,Gly195, and Lys196 are invariant and Thr197 can only be replaced with Ser. The most alterable residue is Gly191, where 10 replacements, even Phe, form a functional enzyme. The remaining positions allow some amino acid replacements while restricting others. The primary structural constraints of the P-loop of the mitochondrial F1 suggests that the three-dimensional structure of the P-loop is similar to that of ras.