Trypanosoma cruzi, the causative agent of Chagas disease, has a dense coat of
GPI-anchored virulence factors. T. cruzi GPI-anchored adhesin GP82 is encoded by
a repertoire of transcripts containing several in-frame initiation codons
located up-stream from that adjacent to the predicted signal peptide (SP).
Transfection of T. cruzi epimastigotes with constructs encoding GP82 starting at
the SP or from the farthest up-stream methionine confirmed protein expression on
the parasite cell surface, comparable to the native GP82. Proteins were fully
functional, inducing parasite adhesion to HeLa cells and lysosome mobilization,
events required for parasite invasion. Transgenic and native GP82 proteins
showed indistinguishable electrophoretic mobility, suggesting similar processing
of the SP. Deletion of SP generated a ~72 kDa protein devoid of N-linked
oligosaccharides allowing irrefutable identification of GP82 precursor. SP
transposition to an internal region of GP82 rendered the signal unrecognizable
by the signal peptidase and incapable to direct the nascent protein for
ER-membrane association. Altogether our data strongly suggests that GP82 SP
fails to function as transmembrane domain and its recognition by the signal
peptidase shows strict dependence on the signal localization at protein
N-terminus. This report presents the first experimental characterization of the
full-length GP82 and its signal peptide.
