The ADP-glucose pyrophosphorylase from Melainabacteria: a comparative study between photosynthetic and non-photosynthetic bacterial sources

María V. Ferretti, Rania A. Hussien, Miguel A. Ballicora, Alberto A. Iglesias, Carlos M. Figueroa, Matías D. Asencion Diez
2021 · doi:10.1101/2021.06.18.448987
preprint OA: closed CC-BY-NC-ND-4.0
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Abstract

Until recently, all members of the cyanobacterial phylum were considered capable of performing oxygenic photosynthesis. This view has been questioned after the discovery of a group of presumed non-photosynthetic cyanobacteria named Melainabacteria . Using metagenomic data, we identified sequences encoding putative ADP-glucose pyrophosphorylase (EC 2.7.7.27, ADP-GlcPPase) from free-living and intestinal Melainabacteria . These genes were de novo synthesized and overexpressed in Escherichia coli . The purified recombinant proteins from the free-living and the intestinal Melainabacteria showed ADP-GlcPPase activity, with V max values of 2.3 and 7.1 U/mg, respectively. Both enzymes had similar affinities towards ATP ( S 0.5 ∼0.3 mM) although the one from the intestinal source displayed a 6-fold higher affinity for glucose-1P. Both recombinant ADP-GlcPPases were sensitive to allosteric activation by glucose-6P ( A 0.5 ∼0.3 mM), and to inhibition by Pi and ADP ( I 0.5 between 0.2 to 3 mM). Interestingly, the enzymes from Melainabacteria were insensitive to 3-phosphoglycerate, which is the principal activator of ADP-GlcPPases from photosynthetic cyanobacteria. To the best of our knowledge, this is the first biochemical characterization of an active enzyme from Melainabacteria , offering further data to discussions regarding their phylogenetic position. This work contributes to a better understanding regarding the evolution of allosteric mechanisms in ADP-GlcPPases, an essential enzyme for the synthesis of glycogen in prokaryotes and starch in plants.

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License: CC-BY-NC-ND-4.0