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

Abstract

The halophilic archaeum, Halobacterium cutirubrum, has been shown to have a cyclophilin-type peptidyl-prolyl cis– trans isomerase (PPIase). Because most archaeal genomes studied only have genes for FK506-binding proteins (FKBPs) as a PPIase, 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 was cloned from genomic DNA of H. cutirubrum and then sequenced. This FKBP was deduced to be composed of 303 amino acid residues with a molecular mass of 33.3 kDa. Alignment of its amino acid sequence with those of other reported FKBPs showed that it contained two insertion sequences in the regions corresponding to the bulge and flap of human FKBP12, which are common to archaeal FKBPs. Its C-terminal amino acid sequence was approximately 130 amino acids longer than the FKBPs of Methanococcus thermolithotrophicus and Thermococcus 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 expressed as a fusion protein with glutathione S-transferase (GST) in Escherichia coli, and the N-terminal GST portion was removed by protease digestion. The purified recombinant FKBP showed a weak PPIase activity with a low sensitivity to FK506. This FKBP suppressed aggregation of the unfolded protein.