Structure and function of trans-sialidase family ; its relation to the parasite lifecycle

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The parasitic Trypanosomes can not synthesize sialic acid but express a unique enzyme, trans-sialidase (TS) in order to incorporate sialic acids on their surface. This enzyme has been shown to be important for parasite to survive in host defense environment and to invade to host cells. The TS are encoded by several gene families and its expression is strongly controlled by stage specific manor.We have presented that TS and parasite surface sialic acids are essential for the African trypanosome Trypanosoma brucei, to protect the parasite from the digestive condition in the mud-gut of Tsetse flies. T.brucei expresses TS at the insect stage. The parasite lacking sialic acids due to a defective generation of GPI-anchored trans-sialidase could not survive in the intestine, but regained the ability to survive when sialylated by means of soluble trans-sialidase.We also have shown that TS in T. cruzi is important for parasite escape from the paraitophorous vacuole (PV). T.cruzi trypomastigotes (TCT) and metacyclic trypomastigotes (MT) attached to and invaded mammalian host cells HeLa or CHO cells equally, but the former TCT escaped from the vacuole earlier than MT. The trypomastigote TS was expressed on the surface of metacyclic formed and used for cell invasion experiments. The transfected parasites could efficiently escaped from the PV and this result indicate that increased TS enzyme activity in TCT is important for efficient earlier exit from the PV to cytoplasm and subsequent differentiation into amastigotes.