On the characterization of ADP-glucose pyrophosphorylase from non-photosynthetic cyanobacteria

FERRETTI, MARÍA V.; BALLICORA, MIGUEL A.; ASENCIÓN DIEZ, MATÍAS D.; IGLESIAS, ALBERTO A.; FIGUEROA, CARLOS M.

Paraná

Congreso; LIV Reunión Anual de la SAIB; 2018

SAIB

Until recently, it was consideredthat all members of the cyanobacterial phylum were capable of performingoxygenic photosynthesis. This view dramatically changed after the discovery ofa group of non-photosynthetic cyanobacteria named Melainabacteria. Usingpublicly available metagenomic data, we identified sequences encoding putativeADP-glucose pyrophosphorylases (EC 2.7.7.27, ADP-GlcPPase) from free-living andintestinal Melainabacteria. The genes coding for these proteins were denovo synthetized and overexpressed in Escherichia coli. Purified enzymesshowed ADP-GlcPPase activity, with Vmax values of 2.3 and 7.1 U/mg for thefree-living and the intestinal Melainabacteria, respectively. Bothenzymes had similar affinities towards ATP (S0.5~ 0.3 mM), although the onefrom intestinal source displayed 6-fold higher affinity for glucose-1P.ADP-GlcPPases are allosteric enzymes regulated by metabolites from the mainroute of carbon utilization in the respective organism. Thus, the enzyme fromphotosynthetic organisms is activated by 3-phosphoglycerate and inhibited byinorganic phosphate. Interestingly, both ADP-GlcPPases from Melainabacteria weremainly activated by glucose-6P (A0.5~ 0.3 mM) but not by 3-phosphoglycerate, whileADP inhibited both enzymes with I0.5 values between 1 and 4 mM. To the best ofour knowledge, this is the first biochemical characterization of a keymetabolic protein from non-photosynthetic cyanobacteria. We consider this workwill contribute to better understand the evolution of allosteric mechanisms inADP-GlcPPases, a critical enzyme for the synthesis of glycogen in bacteria andstarch in plants.