AN INTERNAL FK506-BINDING DOMAIN IS THE CATALYTIC CORE OF THE PROLYL ISOMERASE ACTIVITY ASSOCIATED WITH THE BACILLUS-SUBTILIS TRIGGER FACTOR

Two major families of peptidylprolyl cis-trans-isomerases, the cycloph ilins and the structurally unrelated FK506-binding proteins (FKBPs), h ave been identified as cellular factors involved in protein folding in vitro. Here we report on the biochemical characterization of a second prolyl isomerase of Bacillus subtilis that was purified from a cyclop hilin-negative (ppiB null) mutant and was shown to be the trigger fact or (TigBS). N-terminal sequencing of 27 amino acid residues of the pur ified protein revealed 100% identity to the deduced sequence encoded b y the tig gene, sequenced as a part of the B. subtilis genome project. The tigBS gene, located at 246 degrees on the genetic map upstream of the clpX and lonA,B genes, encodes an acidic protein (pI 4.3) of 47.5 kDa. Purified and recombinant TigBS-His proteins share the same subst rate specificity and catalytic activity (k(cat)/K-m of 1.5 mu M(-1) s( -1)); both are inhibited by the macrolide FK506 with IC50 the range of 500 nM. We also demonstrate that the prolyl isomerase activity of Tig BS is mediated by an internal domain of about 13 kDa (homologous to FK PB12) that represents the catalytic core of the trigger factor.