Functional cooperation between BiP and calreticulin in the folding maturation of a glycoprotein in Trypanosoma cruzi

CARLOS LABRIOLA; ANA VILLAMIL GIRALDO ; ARMANDO PARODI ; JULIO CARAMELO

Salta

Congreso; 3rd Latin American Protein Society; 2010

Latin American Protein Society

Proteins may adopt diverse conformations during their folding in vivo, ranging from extended chains when they emerge from the ribosome to compact intermediates near the end of the folding process. Accordingly, a variety of chaperones and folding assisting enzymes has evolved to deal with this diversity. Chaperone selection by a particular substrate depends on the structural features of its folding intermediates. In addition, this process may be modulated by competitive effects between chaperones. Here we address this issue by using cruzipain (CZ) as model substrate. CZ is an abundant Trypanosoma cruzi lysosomal protease and it was the first identified endogenous UDP-Glc:glycoprotein glucosyltransferase (UGGT) substrate. We found that CZ associated sequentially with BiP and calreticulin (CRT) during its folding process. Early, extended conformations were bound to BiP, while more advanced and compact folding intermediates associated to CRT. The interaction between CZ and CRT was impeded by deletion of the UGGT-encoding gene but, similarly to what was observed in wild type cells, in mutant cells CZ associated to BiP only when displaying extended conformations. The absence of CZ-CRT interactions in UGGT null cells resulted in a drastic reduction of CZ folding efficiency and triggered the aggregation of CZ through intermolecular disulfide bonds. These observations show that BiP and CRT activities complement each other to supervise a complete and efficient CZ folding process. The present report shows that the basic tenets of the quality control mechanism of glycoprotein folding represent an early evolutionary acquisition.