AbstractThe induction of Giardia duodenalis encystment entails an exquisite interplay among transducer elements, which proceeds in a highly ordered manner in response to external stimuli and leads to changes in gene expression. However, little is known about how this parasite transduces the signals of its external environment during encystment. We have identified in Giardia duodenalis protein kinase C-like isoforms (β, δ, ε, θ and ζ) using specific polyclonal antibodies raised against mammalian PKC isoforms, and these proteins showed a differential expression pattern during encystment. Moreover, this kinase family has been shown to have a role during encystment because PKC inhibitors blocked the differentiation process. In particular, the PKCβ-like molecule (gPKCβ) with an atypical high molecular weight (150 kDa), showed a gradual increase in expression during encystment of the parasite and also redistributed from cytoplasm to plasma membrane soon after encystment induction, suggesting that it may play an important role during the differentiation process. Additional biochemical characterization of gPKCβ showed that this isoform displayed in vitro kinase activity dependent on cofactors required by conventional PKCs, i.e. phospholipid, diacylglycerol and calcium. In the Giardia genome database, an ORF that encodes for a homologue of PKCβ catalytic domain was found and cloned. The gPKC features, together with its divergent nature, indicate that this enzyme may constitute a promising target for drug design to block the encystment, and therefore the transmission, of this parasite.