PDILT, a Divergent Testis-specific Protein Disulfide Isomerase with a Non-classical SXXC Motif That Engages in Disulfide-dependent Interactions in the Endoplasmic Reticulum

Abstract

Protein disulfide isomerase (PDI) is the archetypal enzyme involved in the formation and reshuffling of disulfide bonds in the endoplasmic reticulum (ER). PDI achieves its redox function through two highly conserved thioredoxin domains, and PDI can also operate as an ER chaperone. The substrate specificities and the exact functions of most other PDI family proteins remain important unsolved questions in biology. Here, we characterize a new and striking member of the PDI family, which we have named protein disulfide isomeraselike protein of the testis (PDILT). PDILT is the first eukaryotic SXXC protein to be characterized in the ER. Our experiments have unveiled a novel, glycosylated PDI-like protein whose tissue-specific expression and unusual motifs have implications for the evolution, catalytic function, and substrate selection of thioredoxin family proteins. We show that PDILT is an ER resident glycoprotein that liaises with partner proteins in disulfide-dependent complexes within the testis. PDILT interacts with the oxidoreductase Ero1␣, demonstrating that the N-terminal cysteine of the CXXC sequence is not required for binding of PDI family proteins to ER oxidoreductases. The expression of PDILT, in addition to PDI in the testis, suggests that PDILT performs a specialized chaperone function in testicular cells. PDILT is an unusual PDI relative that highlights the adaptability of chaperone and redox function in enzymes of the endoplasmic reticulum.

Efficient IgM assembly and secretion require the plasma cell induced endoplasmic reticulum protein pERp1

“…The PDI family member PDIp is exclusively expressed in the pancreas (19) and PDILT, in testis (20). As a lymphocytespecific protein, pERp1 likely is under control of a transcription factor specific for lymphocyte lineages.…”

A disulfide-bond A oxidoreductase-like protein (DsbA-L) regulates adiponectin multimerization

“…It becomes evident that not all PDIs contains the classic contain classical CXXS motifs. For example, the testis-specific protein disulfide isomerase-like protein (PDILT) contains an SXXS and an SXXC motif (24). The 2 monocysteinic thioredoxins in Arabidopsis thaliana contain the CXXS motif and are very efficient as disulfide isomerases (36).…”

“…These results indicate that DsbA-L plays a selective role in regulating adipokine biosynthesis and secretion. DsbA-L does not have the presumed active site (Cys-Gly-His-Cys) involved in disulfide bond formation, but instead contains a conserved sequence in which the 2 cysteine residues are replaced with serines ( 16 Ser-Pro-Tyr- 19 Ser), which is also found in the testis-specific protein disulfide isomerase-like protein (PDILT) (24) and bacterial HCCA (2-hydroxychromene-2-carboxylate) isomerase, an enzyme involved in bacterial metabolism of naphthalene to salicylate (25) (Fig. S4A).…”

Emerging features of ER resident J-proteins in plants

“…41 For example, PDILT (protein disulphide isomerase-like protein of the testis) has an incomplete active site that lacks the N-terminal cysteine residue, yet is able to form mixed disulfides with partners and substrates in vivo. 42 Despite lacking the CXXC sequence motif, Arabidopsis AtERdj3A protein expressed in Escherichia coli cells retains reductase activity in vitro. 8 AtERdj3A and OsERdj3A have other cysteines in their TRX domains, and it thus remains possible that plant ERdj3As may perform similar functions to mammalian ERdj5.…”