Two strictly polyphosphate-dependent gluco(manno)kinases from diazotrophic Cyanobacteria with potential to phosphorylate hexoses from polyphosphates

Tomás Albi, Aurelio Serrano
2014 Applied Microbiology and Biotechnology  
16 The single-copy genes encoding putative polyphosphate-glucose phosphotransferases (PPGK, EC 17 2.7.1.63) from two nitrogen-fixing Cyanobacteria, Nostoc sp. PCC7120 and Nostoc punctiforme 18 PCC73102, were cloned and functionally characterized. In contrast to their actinobacterial counterparts, 19 the cyanobacterial PPGKs have shown the ability to phosphorylate glucose using strictly inorganic 20 polyphosphates (polyP) as phosphoryl donors. This has proven to be an economically attractive
more » ... ent in 21 contrast to the more costly ATP. Cyanobacterial PPGKs had a higher affinity for medium-long sized 22 polyP (>10 phosphoryl residues). Thus, longer polyP resulted in higher catalytic efficiency. Also in 23 contrast to most their homologs in Actinobacteria, both cyanobacterial PPGKs exhibited a modest but 24 significant polyP-mannokinase activity as well. Specific activities were in the range of 180-230 and 2-3 25 µmol min -1 mg -1 with glucose and mannose as substrates, respectively. No polyP-fructokinase activity 26 was detected. Cyanobacterial PPGKs required a divalent metal cofactor, and exhibited alkaline pH optima 27 (approx. 9.0) and a remarkable thermostability (optimum temperature, 45 ºC). The preference for Mg 2+ 28 was noted with an affinity constant of 1.3 mM. Both recombinant PPGKs are homodimers with a subunit 29 molecular mass of ca. 27 kDa. Based on databases searches and experimental data from Southern blots 30 and activity assays, closely-related PPGK homologs appear to be widespread among unicellular and 31 filamentous mostly nitrogen-fixing Cyanobacteria. Overall, these findings indicate that polyP may be 32 metabolized in these photosynthetic prokaryotes to yield glucose (or mannose) 6-phosphate. They also 33 provide evidence for a novel group-specific subfamily of strictly polyP-dependent gluco(manno)kinases 34 with ancestral features and high biotechnological potential, capable of efficiently using polyP as an 35 alternative and cheap source of energy-rich phosphate instead of costly ATP. Finally, these results could 36 shed new light on the evolutionary origin of sugar kinases. 37 38
doi:10.1007/s00253-014-6184-7 pmid:25381489 fatcat:rx6w5a65dzfszj5h3uljggm2re