Substrate Specificity of the Oxidoreductase ERp57 Is Determined Primarily by Its Interaction with Calnexin and Calreticulin

Abstract

The formation of disulfides within proteins entering the secretory pathway is catalyzed by the protein disulfide isomerase family of endoplasmic reticulum localized oxidoreductases. One such enzyme, ERp57, is thought to catalyze the isomerization of non-native disulfide bonds formed in glycoproteins with unstructured disulfide-rich domains. Here we investigated the mechanism underlying ERp57 specificity toward glycoprotein substrates and the interdependence of ERp57 and the calnexin cycle for their correct folding. Our results clearly show that ERp57 must be physically associated with the calnexin cycle to catalyze isomerization reactions with most of its substrates. In addition, some glycoproteins only require ERp57 for correct disulfide formation if they enter the calnexin cycle. Hence, the specificity of ER oxidoreductases is not only determined by the physical association of enzyme and substrate but also by accessory factors, such as calnexin and calreticulin in the case of ERp57. These conclusions suggest that the calnexin cycle has evolved with a specialized oxidoreductase to facilitate native disulfide formation in complex glycoproteins.

Identification and Characterization of Alternatively Transcribed Form of Peroxiredoxin IV Gene That Is Specifically Expressed in Spermatids of Postpubertal Mouse Testis

“…Indeed, a recent study confirmed that the 27-kDa form of Prx IV is produced as the result of cleavage of the NH 2 -terminal 36 residues of the encoded protein (11). This study also showed, however, that the 27-kDa form of Prx IV is retained within the ER despite the fact that it lacks a recognized ER retention motif (11,12). Both the 27-and 31-kDa forms of Prx IV thus appear to be localized to the ER, whereas other 2-Cys Prx isoforms are located in the cytoplasm (Prxs I and II) or mitochondria (Prx III) (4).…”

“…Prx IV in the ER physically interacts with PDI. Prx IV-S is thus thought to function as a sensor of H 2 O 2 in PDI-mediated protein folding (12,26). Similar to the proposed function of Prx IV-S in the ER, Prx IV-L may sense H 2 O 2 in the cytosol and mediate the formation of disulfide linkages in proteins that participate in chromatin condensation and contribute to the supramolecular structure of the sperm tail.…”

“…A sensor function for 2-Cys Prx has also been demonstrated in yeast (42,43). Such a function for 2-Cys Prx proteins is attributed to the fact that their structure facilitates the reaction of C P -SH with low levels of H 2 O 2 (4, 44 -46) and to their interaction with target molecules such as PDI (12). The presence of Prx IV in the ER and in maturing eutherian male germ cells may thus allow protein disulfide formation without the production of damaging levels of H 2 O 2 .…”

Proteomic analysis of the sheep caruncular and intercaruncular endometrium reveals changes in functional proteins crucial for the establishment of pregnancy

“…This ER-soluble protein interacts with the two lectin chaperones, calreticulin and calnexin, to promote folding of newly synthesised proteins by catalysing the formation of disulphide bonds (Russell et al 2004). ERP57 interacts with glycoproteins during their folding and corrects disulphide bond formation and hence it catalyses the re-folding of mis-folded proteins (Jessop et al 2002). In this study, ERP57 expression increased in the caruncular tissue at the time of implantation and during early pregnancy.…”

The Crystal Structure of the Protein-Disulfide Isomerase Family Member ERp27 Provides Insights into Its Substrate Binding Capabilities

“…ERp57 lacks inherent substrate binding capabilities and interacts with its substrates through the lectins calnexin and calreticulin, which act as adaptors to supply the redox-active site with suitable substrates. The interaction with these lectins primarily determines the substrate specificity of ERp57 (40), which preferentially acts on a glycosylated subset of folding substrates.…”