Study On Function Of Bacterial Tyrosine Kinases And Low-Molecular-Weight Protein Tyrosine Phosphatases In Anabaena Sp. PCC7120

The filamentous cyanobacterium Anabaena sp. PCC7120forms nitrogen-fixing heterocysts after the deprivation of combined nitrogen. Under such conditions, vegetative cells provide heterocysts with carbon compounds and receive fixed nitrogen from the latter.The bacterial tyrosine kinases (BY-kinases) and Low-Molecular-Weight protein tyrosine phosphatases (LWM-PTP) are involved in the biosynthesis of exopolysaccharides in bacteria. We found3genes (alr2856, alr3059and all4432) encoding BY-kinases in the genome of Anabaena sp. PCC7120. Disruption of the one of the3genes (alr2856, alr3059or all4432) did not cause the obvious phenotype after nitrogen step-down.Alr5068, a protein from Anabaena sp. PCC7120, shows significant sequence similarity with LMW-PTPs. In this study the enzymatic properties of Alr5068were characterized and the results showed that it can dephosphorylate several auto-phosphorylated tyrosine kinases (Alr2856, Alr3059and A114432) of Anabaena sp. PCC7120in vitro. Several conserved residues among LMW-PTPs are shown to be essential for the phosphatase activity of Alr5068. The overexpression of alr5068results in a strain unable to survive under diazotrophic conditions, with the formation of morphologically mature heterocysts detached from the filaments. The overexpression of an alr5068allele which losts the phosphatase activity led to the formation of heterocysts with impaired polysaccharide layer. The alr5068gene was up-regulated after nitrogen step-down and its mutation affected the expression of hepA and hepC, two genes necessary for the formation of the heterocyst envelope polysaccharide (HEP) layer.Our results suggest that Alr5068is associated with the production of HEP in Anabaena sp. PCC7120. It offers an insight of the transporting mechanism of heterocyst envelope polysaccharide.