MOLECULAR EVOLUTION OF THE DOMAIN-STRUCTURES OF PROTEIN DISULFIDE ISOMERASES

Protein disulfide isomerase (PDI) is an enzyme that promotes protein f olding by catalyzing disulfide bridge isomerization. PDI and its relat ives form a diverse protein family whose members are characterized by thioredoxin-like (TX) domains in the primary structures. The family wa s classified into four classes by the number and the relative position s of the TX domains. To investigate the evolution of the domain struct ures, we aligned the amino acid sequences of the TX domains, and the m olecular phylogeny was examined by the NJ and ML methods. We found tha t all of the current members of the PDI family have evolved from an an cestral enzyme, which has two TX domains in the primary structure. The diverse domain structures of the members have been generated through domain duplications and deletions.