Protein kinase A activation in lower eukaryotic model systems

MORENO, S.

Rosario, Santa Fe, Argentina

Congreso; 42 Reunion Anual de SAIB,; 2006

SAIB

Our main interest is to understand the mechanism of activation of the cAMP-dependent protein kinase within the cell, contributing to this field with three lower eukaryotic models: the fungus Mucor (M. rouxii and M.racemosus) and Saccharomyces cerevisiae. In Mucor,signal transduction via cAMP exerts a clear physiological effect upon morphology. Biochemical, genetical and physiological approaches have been undertaken with this model. S.cerevisiae has the advantages of its complete genome sequence as well as the tools available both for genetic and biochemical experiments. The protein kinases A (PKA) from both models have been characterized in vitro, and protein substrates have been identified or proposed. The affinities between R and catalytic (C) subunits in both models is completely different as judged by biochemical and genetic parameters, being the affinity between R and C in Mucor PKA much higher. The reasons for the differences in affinities has been approached biochemically, using whole proteins or peptides, genetically and bioinformatically. Activation of yeast PKA has been measured in situ during a physiological increase in cAMP levels; our results show that during this endogenous activation the C subunit (Tpk1) is phosphorylated with a change in its kinetic parameters, and suggest that  only locally produced cAMP can activate the holoenzyme in its endogenous location.