Tandem amino acid repeats from Trypanosoma cruzi shed antigens increase the half-life of proteins in blood

Proteins containing amino acid repeats are widespread among protozoan parasites. It has been suggested that these repetitive structures act as immunomodulators. but other functional aspects may be of primary importance. We have recently suggested that tandem repeats present in Trypanosoma cruzi trans-sialidase stabilize the catalytic activity in blood. Because the parasite releases trans-sialidase, this delayed clearance of the enzyme might have implications in vivo. In the present work, the ability of repetitive units from different T. cruzi molecules in stabilizing trans-sialidase activity in blood was evaluated. It is shown that repeats present on T. cruzi shed proteins (antigens 13 and Shed-Acute-Phase-Antigen [SAPA]) increase trans-sialidase half-life in blood from 7 to almost 35 hours. Conversely, those repeats present in intracellular T. cruzi proteins only increase the enzyme half-life in blood up to 15 hours. Despite these results, comparative analysis of structural and catalytic properties of both groups of chimeric enzymes show no substantial differences. Interestingly, antigens 13 and SAPA also increase the persistence in blood of chimeric glutathione S-transferases. thus suggesting that this effect is inherent to these repeats and independent of the carrier protein. Although the molecular basis of this phenomenon is still uncertain, its biotechnological potential can be envisaged. (C) 1999 by The American Society of Hematology.