Characterization of Agrobacterium tumefaciens PPKs reveals the formation of oligophosphorylated products up to nucleoside nona-phosphates
Celina Frank, Attila Teleki, Dieter Jendrossek
Abstract
Abstract Agrobacterium tumefaciens synthesizes polyphosphate (polyP) in the form of one or two polyP granules per cell during growth. The A. tumefaciens genome codes for two polyphosphate kinase genes, ppk1 AT and ppk2 AT , of which only ppk1 AT is essential for polyP granule formation in vivo. Biochemical characterization of the purified PPK1 AT and PPK2 AT proteins revealed a higher substrate specificity of PPK1 AT (in particular for adenine nucleotides) than for PPK2 AT . In contrast, PPK2 AT accepted all nucleotides at comparable rates. Most interestingly, PPK2 AT catalyzed also the formation of tetra-, penta-, hexa-, hepta-, and octa-phosphorylated nucleosides from guanine, cytosine, desoxy-thymidine, and uridine nucleotides and even nona-phosphorylated adenosine. Our data—in combination with in vivo results—suggest that PPK1 AT is important for the formation of polyP whereas PPK2 AT has the function to replenish nucleoside triphosphate pools during times of enhanced demand. The potential physiological function(s) of the detected oligophosphorylated nucleotides await clarification. Key points • PPK1 AT and PPK2 AT have different substrate specificities, •PPK2 AT is a subgroup 1 member of PPK2s, •PPK2 AT catalyzes the formation of polyphosphorylated nucleosides