Identification and characterization of a sucrose phosphate synthase from Synechococcus sp. pcc 7942

MARTÍNEZ-NOËL G; SALERNO G

Pinamar

Congreso; XLI Reunión Anual SAIB; 2005

SAIB

The salinity tolerance of the freshwater cyanobacterium Synechococcus sp. PCC 7942 is determined by its ability for osmotic adjustment and the presence of sucrose as osmolyte. Sucrose is synthesized in a two-step pathway involving sucrose-phosphate synthase (SPS) and sucrose-phosphate phosphatase (SPP), and hydrolyzed by invertase. The present study describes the first isolation of a SPS encoding gene from a Synechococcus, particularlly, the PCC 7942 strain, and an expression analysis of the gene in the wild type strain and mutant strains. The SPS gene encodes a 88 kDa polypeptide, which is 47% and 45% identical to Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 7002 SPS respectively. Both of them are bidomainal SPSs composed by a Glucosyl- Transferase Domain (GTD) and a Phospho-Hydrolase Domain (PHD). Additionally, sequence analysis of the Synechococcus sp. PCC 7942 genome, revealed that it has no other ORF encoding a putative PHD. This characteristic suggests that SPS from Synechococcus is likely to be a bifuntional enzyme. The fact that the SPS encoding gene was not expressed in mutants impaired in transcriptional factor NtcA or in signal protein PII indicates that sucrose metabolism may be coordinated with nitrogen assimilation through some or both proteins. Supported by ANPCyT (PICT12233), CONICET, UNMdP and FIBA.