Relationship between exopolysaccharide production and protein-tyrosine phosphorylation in gram-negative bacteria

The phosphorylation of proteins at tyrosine residues is known to play a key role in the control of numerous fundamental processes in animal systems. I n contrast, the biological significance of protein-tyrosine phosphorylation in bacteria, which has only been recognised recently, is still unclear. He re, we have analysed the role in Escherichia coli cells of an autophosphory lating protein-tyrosine kinase, Wzc, and a phosphotyrosine-protein phosphat ase, Wzb, by performing knock-out experiments on the corresponding genes, w zc and wzb, and looking at the metabolic consequences induced. The results demonstrate that the phosphorylation of Wzc, as regulated by Wzb, is direct ly connected with the production of a particular capsular polysaccharide, c olanic acid. Thus, when Wzc is phosphorylated on tyrosine, no colanic acid is synthesised by bacteria, but when dephosphorylated by Wzb, colanic acid is produced. This process is rather specific to the pair of proteins Wzc/Wz b. Indeed, a much lesser effect, if any, on colanic acid synthesis is obser ved when knock-out experiments are performed on another pair of genes, etk and etp, which also encode respectively a protein-tyrosine kinase, Etk, and a phosphotyrosine-protein phosphatase, Etp, in E. coli. In addition, the a nalysis of the phosphorylation reaction at the molecular level reveals diff erences between Gram-negative and Gram-positive bacteria, namely in the num ber of protein components required for this reaction to occur. (C) 2000 Aca demic Press.