Peptidyl‐prolyl cis/trans isomerases (PPIases) are enzymes that catalyse protein folding both in vitro and in vivo. We isolated a peptidyl‐prolyl cis/trans isomerase (PPIase) which is specifically associated with the 50S subunit of the Escherichia coli ribosome. This association was abolished by adding at least 1.5 M LiCl. Sequencing the N‐terminal amino acids in addition to three proteolytic fragments totalling 62 amino acids revealed that this PPIase is identical to the E.coli trigger factor. A comparison of the amino acid sequence of trigger factor with those of other PPIase families shows little similarities, suggesting that trigger factor may represent an additional family of PPIases. Trigger factor was purified to homogeneity on a preparative scale from E.coli and its enzymatic properties were studied. In its activity towards oligopeptide substrates, the trigger factor resembles the FK506‐binding proteins (FKBPs). Additionally, the pattern of subsite specificities with respect to the amino acid preceding proline in Suc‐Ala‐Xaa‐Pro‐Phe‐4‐nitroanilides is reminiscent of FKBPs. However, the PPIase activity of the trigger factor was not inhibited by either FK506 or by cyclosporin A at concentrations up to 100 microM. In vitro, the trigger factor catalysed the proline‐limited refolding of a variant of RNase T1 much better than all other PPIases that have been examined so far.

The reversible protein phosphorylation on serine or threonine residues that precede proline (pSer/Thr-Pro) is a key signaling mechanism for the control of various cellular processes, including cell division. The pSer/Thr-Pro moiety in peptides exists in the two completely distinct cis and trans conformations whose conversion is catalyzed specifically by the essential prolyl isomerase Pin1. Previous results suggest that Pin1 might regulate the conformation and dephosphorylation of its substrates. However, it is not known whether phosphorylation-dependent prolyl isomerization occurs in a native protein and/or affects dephosphorylation of pSer/Thr-Pro motifs. Here we show that the major Pro-directed phosphatase PP2A is conformation-specific and effectively dephosphorylates only the trans pSer/Thr-Pro isomer. Furthermore, Pin1 catalyzes prolyl isomerization of specific pSer/Thr-Pro motifs both in Cdc25C and tau to facilitate their dephosphorylation by PP2A. Moreover, Pin1 and PP2A show reciprocal genetic interactions, and prolyl isomerase activity of Pin1 is essential for cell division in vivo. Thus, phosphorylation-specific prolyl isomerization catalyzed by Pin1 is a novel mechanism essential for regulating dephosphorylation of certain pSer/Thr-Pro motifs.

The peptidyl prolyl cis/trans isomerase Pin1 has been implicated in the development of cancer, Alzheimer's disease and asthma, but highly specific and potent Pin1 inhibitors remain to be identified. Here, by screening a combinatorial peptide library, we identified a series of nanomolar peptidic inhibitors. Nonproteinogenic amino acids, incorporated into 5-mer to 8-mer oligopeptides containing a d-phosphothreonine as a central template, yielded selective inhibitors that blocked cell cycle progression in HeLa cells in a dose-dependent manner.

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A low degree of amino acid sequence similarity to FK506-binding proteins (FKBPs) has been obtained for the peptidyl prolyl cis/trans isomerase (PPIase) domain of E. coli trigger factor (TF) that was thought to be significant with regard to the enzymatic properties of the bacterial enzyme. We examined whether the alteration of a negatively charged side-chain at position 37 (FKBP numbering) and a phenylalanine at position 99, both highly conserved through both types of enzymes, leads to parallel effects on the catalytic activity of both FKBP12 and TF-PPIase domain in a series of tetrapeptide substrates with different P1 subsites. For the latter enzyme, substitution of Glu178 by Val or Lys, which aligns to Asp37 in human FKBP12, enhanced the PPIase activity, whereas a strongly decreased enzymatic activity was determined for the Asp37Leu and Asp37Val variants of FKBP12. Regardless of the P1 subsite of the substrate used for the assay, mutation of Phe233Tyr generated a protein variant of the TF-PPIase domain with about 1% of the wild type PPIase activity. Dependent on the substrate nature, a moderate decrease as well as a 4.8-fold increase in k(cat)/K(M) could be determined for the corresponding Phe99Tyr FKBP12 variant. Neither of the mutations of the TF-PPIase domain was able to implant FK506 inhibition found as a major characteristic of the FKBP family of PPIases.

A functionally Pin1-like peptidyl-prolyl cis/trans isomerase (PPIase 1 ) was isolated from proembryogenic masses (PEMs) of Digitalis lanata according to its enzymatic activity. Partial sequence analysis of the purified enzyme (DlPar13) revealed sequence homology to members of the parvulin family of PPIases. Similar to human Pin1 and yeast Ess1, it exhibits catalytic activity toward substrates containing (Thr(P)/Ser(P))-Pro peptide bonds and comparable inhibition kinetics with juglone. Unlike Pin1-type enzymes it lacks the phosphoserine or phosphothreonine binding WW domain. Western blotting with anti-DlPar13 serum recognized the endogenous form in nucleic and cytosolic fractions of the plant cells. Since the PIN1 homologue ESS1 is an essential gene, complementation experiments in yeast were performed. When overexpressed in Saccharomyces cerevisiae DlPar13 is almost as effective as hPin1 in rescuing the temperature-sensitive phenotype caused by a mutation in ESS1. In contrast, the human parvulin hPar14 is not able to rescue the lethal phenotype of this yeast strain at nonpermissive temperatures. These results suggest a function for DlPar13 rather similar to parvulins of the Pin1-type.Human Pin1 belongs to the parvulin family of peptidyl-prolyl cis/trans isomerases (EC 5.2

We identified a periplasmic peptidyl-prolyl cis/transisomerase (PPIase) of the (FK506-binding protein (FKBP) type in Escherichia coli (FK506 represents a natural peptidomacrolide containing an acylated pipecolic acid residue). After purification to homogeneity, its complete amino acid sequence was determined by a combination of Edman degradation and electrospray mass spectrometry of the authentic protein and peptides generated by proteolysis. The molecular mass calculated from the amino acid sequence of the protein was 22,085.53 Da, which corresponded perfectly with the value of 22,084 ؎ 1.47 Da as determined by mass spectrometry. The corresponding gene was cloned and analyzed, and Southern blot experiments revealed the existence of similar genes in various Gram-negative bacteria. The amino acid sequence of the novel FKBP22 shows similarity to Mip (macrophage infectivity potentiator)-like proteins produced by a number of pathogenic bacteria. However, FKBP22 is inhibited more strongly by FK506 than are other Mip-homologues, as indicated by the K i value of 25 nM. The subsite specificity regarding the P 1 position of the substrate resembles that for Mip-FKBP25 from Legionella pneumophila. The mature FKBP22 enzyme of 205 amino acids exists as a dimer in solution.The observation of an accelerated cis/trans isomerization of the oligopeptide succinyl-Ala-Ala-Pro-Phe-4-nitroanilide in biological material led to the discovery of peptidyl-prolyl cis/ trans-isomerases (PPIases, E.C. 5.2.1.8) 1 in 1984 (1). Recently, it was shown that they can also act on polypeptides as folding helper enzymes during the refolding of proteins in vitro (2) and in vivo (3,4). By comparison of their amino acid sequences PPIases can be subdivided into three families: the cyclophilins (5), the FK506-binding proteins (FKBPs) (6), and the parvulins (7,8). The families consist of many different members even in the same cell type or organism (9, 50). Little data exist describing the occurrence of Mip-like proteins or PPIases of the FKBP family in Enterobacteriaceae such as Escherichia coli. In addition to two members of the cyclophilin family of PPIases, E. coli also contains the 10.1-kDa PPIase parvulin (7), the 48-kDa trigger factor (21), and three FKBP-like genes. The predicted protein product of one open reading frame, orf149, shows similarities to the FKBPs (22). The slyD gene (23) and its protein product (24) is 47.3% similar to the FKBP family but the protein does not exhibit PPIase activity in the standard enzyme assay. The amino acid sequence deduced from the recently discovered fkpA gene is much more related to the Mip-like FKBPs (25), showing 83% identity to the consensus sequence of the catalytic core as derived by Trandinh et al. (26). In all these cases, it remains unclear whether or not the deduced proteins have PPIase activity and contribute to the PPIase pattern of E. coli.In this study we describe the purification and characterization of a new periplasmic, Mip-like PPIase from E. coli, and show that similar genes are present in ot...

The 48 kDa trigger factor (TF) of E. coli was shown to be a peptidyl-prolyl cisltrans isomerase (PPIase). Its location on a ribosomal particle is unique among the PPIases described so far, and suggests a role in de novo protein folding. The trigger factor was investigated with regard to a domain carrying the catalytic activity. An enzymatieally active fragment could be isolated after proteolysis by subtifisin. The resulting polypeptide was analysed by N-terminal sequencing and MALDI-TOF mass spectrometry revealing an 11.8 kDa fragment of TF encompassing the amino acid residues Arg-145 to Glu-251. The nucleotide sequence encoding the amino acid residues Met-140 to Ala-250 of the TF was cloned into vector pQE32. After expression in E. coli the resulting His-tagged polypeptide was isolated on an Ni 2+-NTA column. Subsequent digestion with subtifisin and anionexchange chromatography yielded a TF fragment encompassing amino acids Gin-148 to Thr-249. This fragment may represent the catalytic core of TF since PPIase activity with a specificity constant kcat/Km of 1.3 ~1-1 s -l could be demonstrated when using Suc-Ala-Phe-Pro-Phe-NH-Np as a substrate. Moreover, as was observed for the complete, authentic TF the PPIase activity of the fragment was not inhibited by the peptidomacrofide FK506.