Regulation of Ca2+/calmodulin-dependent protein kinase from Trypanosoma cruzi

Abstract

A multifunctional Ca2+/calmodulin-dependent protein kinase (TcCaM K) was purified and characterized from the cytosol of Trypanosoma cruzi epimastigote forms. Like mammalian CaM KII, TcCaM K has a broad substrate specificity and a similar subunit composition. Western blot analysis revealed that this TcCaM K possesses two subunits of 50 and 60 kDa, which exhibited autophosphorylating activity. A panel of monoclonal and polyclonal antibodies raised against rat brain CaM KII could also recognize TcCaM K. However, experimental evidence suggests a different conformational arrangement of the TcCaM K subunits. Like its mammalian counterpart, two highly active autonomous, Ca2+-independent, states of TcCaM K can be isolated. These states, caused by high phosphate incorporation, differ only in their extent of Ca2+/CaM-dependence. About 15–20% of the autophosphorylated TcCaM K can be reverted using protein phosphatase 2A, and, consequently, its Ca2+-dependent activity is also partially restored. The situation is somewhat different when the enzyme is linked to the cytoskeleton, as we have previously shown. The membrane-bound form is present only in the native form. Activation increases its protein kinase activity from 5- to 14-fold. In this study, we provide evidence of another form of TcCaM K present in soluble fractions of the parasite that can be isolated in autonomous states. Our results suggest that autophophorylation of membrane-bound TcCaM K may be responsible for kinase release in a Ca2+/CaM-independent state. These properties of TcCaM K may play an important role in regulating Ca2+-dependent processes in the parasite.