Identification of Genes and Functional Characterization of Proteins Involved in Polyphosphate Metabolism in Photosynthetic Organisms

Abstract

A comprehensive survey of genes presumably involved in polyP metabolism was carried out with photosynthetic organisms, both prokaryo-tes and eukaryotes. Photosynthetic bacteria exhibit single genes encoding polyP-kinase (PPK) and exopolyphosphatase (PPX) of the PPX-GPPA family , although paralogous genes are found in some species. Cyanobacteria exhibit multi-domain PPXs containing an extra HD-phosphohydrolase domain, N2-fixing strains having in addition single genes for polyP-glucokinase. The cyanobacterial genes are transcriptionally regulated. Diverse photosyn-thetic eukaryotes have genes encoding bacterial PPX and PPK orthologues. Algal genes for a non-homologous PPX of the DHH-DHHA2 phos-phoesterase family and a closely related family II pyrophosphatase, not previously reported in phototrophs and eukaryotes respectively, were also found. Many of these genes were functionally validated by heterologous expression and the encoded proteins biochemically characterized.