Identification and characterization of a periplasmic phosphate-binding protein in phosphorus-starved Pyropia yezoensis

The synthesis of several polypeptides (145, 76, 66, 52, 42, 32, and 16 kDa) in Pyropia yezoensis was markedly induced under phosphorus-starved conditions. The most abundant 32-kDa polypeptide was purified and characterized. Comparison of the genomic and cDNA sequences revealed an intronless gene encoding a 323-amino-acid precursor protein with a 24-amino-acid signal peptide and a 299-amino-acid mature protein. The mature 32-kDa polypeptide showed high sequence similarity to periplasmic phosphate-binding proteins (PBPs) from Escherichia coli and marine cyanobacteria. Both the native and recombinant proteins exhibited phosphate-binding ability in equilibrium dialysis assays. Immunological analyses indicated that the phosphorus-starvation-induced 32-kDa PBP is localized to the periplasmic space. Northern blot and quantitative real-time PCR analyses demonstrated that PBP gene expression was strongly induced by phosphorus starvation. These findings support a model of phosphate acquisition in P. yezoensis under phosphorus-starved conditions involving a periplasmic PBP and alkaline phosphatase.