Two thioredoxin-superfamily members from sea bass (Dicentrarchus labrax, L.): characterization of PDI (PDIA1) and ERp57 (PDIA3)

PDI (PDIA1) and ERp57 (PDIA3), members of the PDI family and of the thioredoxin (Trx) superfamily, are multifunctional proteins with wide physiological roles and have been implicated in several pathologies. Importantly, they are both involved in the MHC class I antigen presentation pathway. This paper reports the isolation and characterization of full cDNA and genomic clones from sea bass (Dicentrarchus labrax, L.) PDI (Dila-PDI) and ERp57 (Dila-ERp57). The genes are ~12.4 and ~7.1 kb long, originating 2155 and 2173 bp transcripts and encoding 497 and 484 amino acids mature proteins, for Dila-PDI and -ERp57, respectively. The PDI gene consists of eleven exons and ERp57 of thirteen. As described in other species, both molecules are composed of four Trx-like domains (abb'a') followed by a C-terminal tail, retaining two CGHC active sites and an ER-signalling sequence, suggestive of a conserved function. Additionally, three-dimensional homology models further support Dila-PDI and Dila-ERp57 as orthologs of mammalian PDI and ERp57, respectively. Finally, high similarity is observed to their vertebrate counterparts (>69% identity), especially among the few ones from closely related teleosts (>79% identity). Hence, these results provide relevant primary data and will enable further studies to clarify the roles of PDI and ERp57 in European sea bass immunity.