CDNA CLONING AND BACULOVIRUS EXPRESSION OF THE HUMAN LIVER ENDOPLASMIC-RETICULUM P58 - CHARACTERIZATION AS A PROTEIN DISULFIDE-ISOMERASE ISOFORM, BUT NOT AS A PROTEASE OR A CARNITINE ACYLTRANSFERASE

The function of a 58-kDa liver microsomal protein (P58) is controversi al. To help clarify the physiological function of this protein, partic ularly in humans, a full-length human liver cDNA clone was isolated, s equenced, and expressed in milligram quantities with the use of a bacu lovirus expression system, The deduced amino acid sequence of the matu re protein contained two thioredoxin-like active site motifs (CGHC) an d in its C-terminus a nuclear localization motif (KPKKKKK), and an ER- retention/retrieval motif (QEDL). The mature form of human P58 shared 95% amino acid sequence identity with the deduced amino acid sequences of a bovine liver cDNA, 93% with a murine B lymphocyte cDNA, and 91% with a rat basophilic leukemia cell cDNA, In contrast to reports on th e activities of nonhuman forms of P58, the purified expressed human P5 8 showed no carnitine acyltransferase or protease activities. However, it did have protein disulfide isomerase activity, indicating that the physiological activity of human liver P58 may be attributed, at least in part, to this activity. (C) 1995 Academic Press, Inc.