Biosynthesis of the major surface protease GP63 of Leishmania chagasi.

The protozoan Leishmania chagasi expresses a surface metalloprotease, GP63, whose abundance increases 14-fold as parasites grow from logarithmic to stationary phase. L. chagasi GP63 is encoded by three classes of MSP genes that are differentially expressed during parasite growth. Using metabolic labeling and immunoprecipitation, we found L. chagasi GP63 first appeared as a 66-kDa band that was replaced by a 63-kDa protein. This pattern also occurred in transfected L. donovani harboring detectable products of only one MSP gene, suggesting a precursor-product relationship. The half-life of GP63 increased from 29 h in logarithmic phase to >72 h in stationary phase promastigotes. GP63 loss from the cell was complemented by the appearance of a 63-kDa GP63 in extracellular medium in both membrane-associated and -free forms. Calculations suggested that the long and lengthening T(1/2) of cell-associated GP63 accounts in part for its progressive accumulation in the cell during promastigote growth. The current findings add yet another level of complexity to post-transcriptionally regulated expression of an abundant surface molecule in a trypanosomatid protozoan.