Descriptive and functional analyses of four cyclin proteins in Trichomonas vaginalis

Trichomonas vaginalis is an early divergent protozoan parasite that causes trichomoniasis, the most common non-viral sexually transmitted infection. In metazoans, there is abundant and detailed research on the cell cycle and the components involved in the regulation mechanisms. Regulators such as the cyclin-dependent kinases (CDKs) and cyclins activate the highly regulated processes of cell division. While CDKs have important roles in the phosphorylation of specific substrates, cyclins are important activating-components of CDKs that allow orderly passage through the different stages of the cell cycle. Cell cycle cyclins are characterized by showing drastic changes in their concentration during the cell cycle progression. However, in protists such as T. vaginalis, some biological processes such as cell cycle regulation remain less well studied. In an attempt to gain insight into cell cycle regulation in T. vaginalis, as an initial approach we characterized four proteins with features of cyclins. The genes encoding these putative cyclins were cloned to produce the recombinant proteins TvCYC1, TvCYC2, TvCYC3, and TvCYC4. The functional activity of TvCYC2, TvCYC3, and TvCYC4 was assessed through their complementation of a yeast cln1,2,3Δ mutant strain; TvCYC1 was not able to complement this mutant. Furthermore, our results suggest that TvCYC1, TvCYC2, and TvCYC3, are able to interact with and activate the kinase activity of TvCRK1, a kinase previously characterized by our group. The present study represents the first characterization of cyclins potentially involved in cell cycle regulation in T. vaginalis.