Sucrose biosynthesis by a single bidomainal protein

MARTINEZ NOEL, G; CUMINO, AC; KOLMAN, MA; SALERNO, G

Rodhe Island, Providence

Congreso; Plant Biology 2013; 2013

American Society of Plant Biologists

In plants and cyanobacteria, the net synthesis ofsucrose is catalysed by a two-step pathway.From UDP-Glc (or ADP-Glc) and fructose-6P,sucrose-phosphate synthase (SPS) producessucrose-6P, which is dephosphorylated bysucrose-phosphate phosphatase (SPP). Studiesin Anabaena (Nostoc) sp. PCC 7120 showed that7120-SPS and 7120-SPP define two independentminimal catalytic units. Bidomainal SPSs, whereboth units are fused, occur in plants andcyanobacteria, but they display only SPSactivity. The aim of this work was to analyse thepotential of bidomainal SPSs to achieve netsucrose synthesis, by studying: i) chimericalproteins generated by the fusion of functional7120-SPS and 7120-SPP; ii) a comprehensiveanalysis on cyanobacterial sequences encodingputative bidomainal SPSs; and iii) the functionalcharacterisation of SPS from the unicellularstrain Synechococcus elongatus PCC 7942. Wedemonstrated that the bidomainal chimerasdisplay both SPS and SPP activity and that thearrangement 7120-SPS/SPP is the most efficientto yield sucrose. Also we present the firstevidence of a bidomainal/bifunctional SPSpresent in the cyanobacterium S. elongatus PCC7942. Our results indicate that sucrose enzymesmay have evolved keeping its functionalmodularity. While in most cyanobacterialstrains, similarly to plants, sucrose-6Pchannelling may be taking place as the result ofthe interaction between bidomainal SPSsharboring a non-active SPP-module and anindependent SPP protein, in other strains theintramolecular channelling of the intermediate ina bifunctional SPS protein leads to an efficientsucrose synthesis.