Title: A polyphosphate kinase (PPK2) widely conserved in bacteria
Abstract: Synthesis of inorganic polyphosphate (poly P) from the terminal phosphate of ATP is catalyzed reversibly by poly P kinase (PPK, now designated PPK1) initially isolated from Escherichia coli . PPK1 is highly conserved in many bacteria, including some of the major pathogens such as Pseudomonas aeruginosa . In a null mutant of P. aeruginosa lacking ppk1 , we have discovered a previously uncharacterized PPK activity (designated PPK2) distinguished from PPK1 by the following: synthesis of poly P from GTP or ATP, a preference for Mn 2+ over Mg 2+ , and a stimulation by poly P. The reverse reaction, a poly P-driven nucleoside diphosphate kinase synthesis of GTP from GDP, is 75-fold greater than the forward reaction, poly P synthesis from GTP. The gene encoding PPK2 ( ppk2 ) was identified from the amino acid sequence of the protein purified near 1,000-fold, to homogeneity. The 5′-end is 177 bp upstream of the annotated genome sequence of a “conserved hypothetical protein”; ppk2 (1,074 bp) encodes a protein of 357 aa with a molecular mass of 40.8 kDa. Sequences homologous to PPK2 are present in two other proteins in P. aeruginosa , in two Archaea, and in 32 other bacteria (almost all with PPK1 as well); these include rhizobia, cyanobacteria, Streptomyces , and several pathogenic species. Distinctive features of the poly P-driven nucleoside diphosphate kinase activity and structural aspects of PPK2 are among the subjects of an accompanying report.