A DING phosphatase in Thermus thermophilus

Phosphate transport in bacteria occurs via a phosphate specific transporter system (PSTS) that belongs to the ABC family of transporters, a multisubunit system, containing an alkaline phosphatase. DING proteins were characterized due to the N-terminal amino acid sequence DINGG GATL, which is highly conserved in animal and plant isolates, but more variable in microbes. Most prokaryotic homologues of the DING proteins often have some structural homology to phosphatases or periplasmic phosphate-binding proteins. In E. coli , the product of the inducible gene Din G, possesses ATP hydrolyzing helicase enzymic activity. An alkaline phosphorolytic enzyme of the PSTS system was purified to homogeneity from the thermophilic bacterium Thermus thermophilus . N-terminal sequence analysis of this protein revealed the same high degree of similarity to DING proteins especially to the human synovial stimulatory protein P205, the steroidogenesis-inducing protein and to the phosphate ABC transporter, periplasmic phosphate-binding protein, putative ( P. fluorescens Pf-5). The enzyme had a molecular mass of 40 kDa on SDS/PAGE, exhibiting optimal phosphatase activity at pH 12.3 and 70 °C. The enzyme possessed characteristics of a DING protein, such as ATPase, ds endonuclease and 3′ phosphodiesterase (3′-exonuclease) activities and binding to linear dsDNA, displaying helicase activity on supercoiled DNA. Purification and biochemical characterization of a T. thermophilus DING protein was achieved. The biochemical properties, N-terminal sequence similarities of this protein implied that the enzyme belongs to the PSTS family and might be involved in the DNA repair mechanism of this microorganism.