2 research outputs found
Two strictly polyphosphate-dependent gluco(manno)kinases from diazotrophic Cyanobacteria with potential to phosphorylate hexoses from polyphosphates
The single-copy genes encoding putative
polyphosphate–glucose phosphotransferases (PPGK, EC
2.7.1.63) from two nitrogen-fixing Cyanobacteria, Nostoc
sp. PCC7120 and Nostoc punctiforme PCC73102, were
cloned and functionally characterized. In contrast to their
actinobacterial counterparts, the cyanobacterial PPGKs have
shown the ability to phosphorylate glucose using strictly
inorganic polyphosphates (polyP) as phosphoryl donors.
This has proven to be an economically attractive reagent in
contrast to the more costly ATP. Cyanobacterial PPGKs had a
higher affinity for medium–long-sized polyP (greater than ten
phosphoryl residues). Thus, longer polyP resulted in higher
catalytic efficiency. Also in contrast to most their homologs in
Actinobacteria, both cyanobacterial PPGKs exhibited a modest
but significant polyP-mannokinase activity as well.
Specific activities were in the range of 180–230 and 2–
3 μmol min−1 mg−1 with glucose and mannose as substrates,
respectively. No polyP-fructokinase activity was detected.
Cyanobacterial PPGKs required a divalent metal cofactor
and exhibited alkaline pH optima (approx. 9.0) and a remarkable
thermostability (optimum temperature, 45 °C). The preference
for Mg2+ was noted with an affinity constant of
1.3 mM. Both recombinant PPGKs are homodimers with a
subunit molecular mass of ca. 27 kDa. Based on database
searches and experimental data from Southern blots and activity assays, closely related PPGK homologs appear to be
widespread among unicellular and filamentous
mostly nitrogen-fixing Cyanobacteria. Overall, these findings
indicate that polyP may be metabolized in these photosynthetic
prokaryotes to yield glucose (or mannose) 6-phosphate.
They also provide evidence for a novel group-specific subfamily
of strictly polyP-dependent gluco(manno)kinases with
ancestral features and high biotechnological potential, capable
of efficiently using polyP as an alternative and cheap source of
energy-rich phosphate instead of costly ATP. Finally, these
results could shed new light on the evolutionary origin of
sugar kinasesPeer reviewe