SUCROSE-PHOSPHATE PHOSPHATASE ACTIVITY IN SYNECHOCOCCUS SP. PCC 7942

MARTÍNEZ-NOËL G; SALERNO G

Santa Fe, Argentina

Congreso; SAIB; 2006

SAIB

The biosynthesis of sucrose (Suc) occurs through the concomitant action of sucrose-phosphate synthase (SPS) and sucrose-phosphate phosphatase (SPP). In unicellular cyanobacteria, the SPS protein exhibits a two domain arrangenment containing a glucosyl-transferase domain (GTD) and a phosphohydrolase domain (PHD), at the Nt and Ct regions, respectively. In the freshwater cyanobacterium Synechococcus sp. PCC 7942, we firstly demonstrated the presence of Suc, and we also showed that the open reading frame Selo020095 encodes a protein with SPS activity (named 7942-SPS) by expression in Escherichia coli. After sequence analysis of the Synechococcus sp. genome, we did not find any independent sequence of a putative phosphohydrolase (corresponding to a SPP-like protein) as there is present in other unicellular cyanobacteria. By in silica analysis of the deduced amino acid sequence of 7942-SPS, we determined that the reported crucial amino acids for a functional SPP (Asp 9-Asp 11) are present in the PHD domain of the protein. Therefore, we used different biochemical approaches to evaluate whether 7942-SPS may have also SPP activity. The results seems to indicate that a unique protein could catalyze not only the glucosyl transferase reaction but also the dephosphorylation of the intermediate (Suc-6P). This finding is very important to understand the evolution of the Suc biosynthesis enzymes.