Polyphosphate(polyP) polymerase domain of yeast vacuolar transport chaperone (VTC) proteins VTC-2, and -3 , and similar proteins.
Saccharomyces cerevisiae VTC-1, -2, -3, and -4 comprise the membrane-integral VTC complex. VTC-2, -3, and -4 contain polyP polymerase domains. S. cerevisiae VTC-2,and -3 belong to this subgroup. For VTC4 it has been shown that this domain generates polyP from ATP by a phosphotransfer reaction releasing ADP. This activity is metal ion-dependent. The ATP gamma phosphate may be cleaved and then transferred to an acceptor phosphate to form polyP. PolyP is ubiquitous. In prokaryotes, it is a store of phosphate and energy. In eukaryotes, polyPs have roles in bone calcification, and osmoregulation, and in phosphate transport in the symbiosis of mycorrhizal fungi and plants. This subgroup belongs to the CYTH/triphosphate tunnel metalloenzyme (TTM)-like superfamily, whose enzymes have a unique active site located within an eight-stranded beta barrel.