Polyphosphate polymerizing and depolymerizing activity of VTC4 protein in an arbuscular mycorrhizal fungus

Arbuscular mycorrhizal (AM) fungi form symbiotic associations with land plants and supply soil minerals including phosphorus to their hosts. AM accumulate polyphosphate (polyP), a linear phosphate polymer, in mycelia, which functions storage translocation. In the budding yeast Saccharomyces cerevisiae, it has been demonstrated that vacuolar transporter chaperone 4 (VTC4) protein, subunit of VTC complex, is responsible for polyP synthesis. Here, we conducted comprehensive survey proteins eight fungal genomes by Blast analysis characterized biochemical properties Rhizophagus irregularis VTC4. The species encode VTC1, VTC2, recombinant protein RiVTC4* (RiVTC4183–474) containing catalytic tunnel domain was expressed E. coli cells purified. capable catalyzing polymerization using ATP as substrate. Pyrophosphate enhanced polyP-polymerizing activity >10-fold. exhibited maximum at neutral pH required divalent metal ions, preferentially Mn2+. presence high concentrations ADP, reverse reaction (the regeneration from polyP) occurred. range 0.2–5 mM depolymerization observed ATP/ADP ratio less than 2–5. These results suggest VTC4 not only synthesizes but also regenerates potential implications modulation levels fungi.