FK506-binding protein-type peptidyl-prolyl cis-trans isomerase from a halophilic archaeum, Halobacterium cutirubrum

The halophilic archaeum, Halobacterium cutirubrum, has been shown to have a cyclophilin-type peptidyl-prolyl cis-trans isomerase (PPIase). Because mos t archaeal genomes studied only have genes for FK506-binding proteins (FKBP s) as a FPIase, it has been unclear whether H. cutirubrum has an FKBP-type PPIase or not. In the present study, a gene encoding an FKBP-type PPIase wa s cloned from genomic DNA of H. cutirubrum and then sequenced. This FKBP wa s deduced to be composed of 303 amino acid residues with a molecular mass o f 33.3 kDa. Alignment of its amino acid sequence with those of other report ed FKBPs showed that it contained two insertion sequences in the regions co rresponding to the bulge and flap of human FKBP12, which are common to arch aeal FKBPs. Its C-terminal amino acid sequence was approximately 130 amino acids longer than the FKBPs of Methanococcus thermolithotrophicus and Therm ococcus sp. KS-1. Among the 14 conserved amino acid residues that form the FK506 binding pocket, only three were found in this FKBP. This gene was exp ressed as a fusion protein with glutathione S-transferase (GST) in Escheric hia coli, and the N-terminal GST portion was removed by protease digestion. The purified recombinant FKBP showed a weak PPIase activity with a low sen sitivity to FK506. This FKBP suppressed aggregation of the unfolded protein . (C) 2000 Elsevier Science B.V. All rights reserved.