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Vol. 14, Issue 9, 3529-3540, September 2003

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The Interplay between Folding-facilitating Mechanisms in Trypanosoma cruzi Endoplasmic Reticulum

Ianina Conte ^*, Carlos Labriola ^*, Juan J. Cazzulo ^*, Roberto Docampo , and Armando J. Parodi ^* 

^* Institute for Biotechnological Research, University of San Martin, CC30, (1650) San Martin, Argentina; Department of Pathobiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61802-6178

Submitted April 14, 2003; Revised May 15, 2003; Accepted May 22, 2003
Monitoring Editor: Reid Gilmore

Lectin (calreticulin [CRT])-N-glycan–mediated quality control of glycoprotein folding is operative in trypanosomatid protozoa but protein-linked monoglucosylated N-glycans are exclusively formed in these microorganisms by UDP-Glc:glycoprotein glucosyltransferase (GT)-dependent glucosylation. The gene coding for this enzyme in the human pathogen Trypanosoma cruzi was identified and sequenced. Even though several of this parasite glycoproteins have been identified as essential components of differentiation and mammalian cell invasion processes, disruption of both GT-encoding alleles did not affect cell growth rate of epimastigote form parasites and only partially affected differentiation and mammalian cell invasion. The cellular content of one of the already identified T. cruzi glycoprotein virulence factors (cruzipain, a lysosomal proteinase) only showed a partial (5–20%) decrease in GT null mutants in spite of the fact that >90% of all cruzipain molecules interacted with CRT during their folding process in wild-type cells. Although extremely mild cell lysis and immunoprecipitation procedures were used, no CRT-cruzipain interaction was detected in GT null mutants but secretion of the proteinase was nevertheless delayed because of a lengthened interaction with Grp78/BiP probably caused by the detected induction of this chaperone in GT null mutants. This result provides a rationale for the absence of a more drastic consequence of GT absence. It was concluded that T. cruzi endoplasmic reticulum folding machinery presents an exquisite plasticity that allows the parasite to surmount the absence of the glycoprotein-specific folding facilitation mechanism.

Abbreviations used: CNX, calnexin; CRT, calreticulin; CZP, cruzipain; DNJ, deoxynojirimycin; ER, endoplasmic reticulum; GI, glucosidase I; GII, glucosidase II; Grp78/BiP, glucose regulated protein 78/immunoglobulin binding protein; GT, UDP-Glc:glycoprotein glucosyltransferase; SDS-PAGE, sodium dodecylsulfate-polyacrylamide gel electrophoresis.

Corresponding author. E-mail address: aparodi{at}leloir.org.ar.

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