Stage-specific regulation of protein phosphorylation in Leishmania major

We investigated whether there are changes in protein phosphorylation or protein kinase activities during the life cycle of Leishmania major. Using a kinase renaturation assay, we detected several leishmanial kinases at each stage of the life cycle. In particular we identified a 50-kDa kinase that is active in procyclic and metacyclic parasites but is inactive in amastigotes. An in vitro phosphorylation assay demonstrated that the pattern of serine and threonine phosphorylated proteins was regulated during the leishmanial life cycle; specifically changes in the phosphorylation of a 108-, a 62-, a 52- and a 49-kDa protein were detected. We present evidence that suggests that changes in phosphorylation of the 108-, 62- and 52-kDa proteins are due to the activity of one or more amastigote specific phosphatases. No differences were detectable in the relative ratios of phosphorylation on serine, threonine, and tyrosine residues in lysates from the different stages. In addition, the pattern of tyrosine phosphorylated proteins in lysates from different L. major developmental stages was similar as detected with a commercial antibody to phosphotyrosine. A 37-kDa phosphorylated protein reacted strongly with the antibody and comigrated with a 37-kDa protein identified in the in vitro phosphorylation assay. Our results support the hypothesis that protein phosphorylation plays an important role in signal transduction pathways in Leishmania major.