Peptidylprolylisomerases,Protein Folders,or Scaffolders? The Example of FKBP51 and FKBP52

Peptidylprolyl-isomerases (PPIases) comprise of the protein families of FK506 binding proteins (FKBPs), cyclophilins, and parvulins. Their common feature is their ability to expedite the transition of peptidylprolyl bonds between the cis and the trans conformation. Thus, it seemed highly plausible that PPIase enzymatic activity is crucial for protein folding. However, this has been difficult to prove over the decades since their discovery. In parallel, more and more studies have discovered scaffolding functions of PPIases. This essay discusses the hypothesis that PPIase enzymatic activity might be the consequence of binding to peptidylprolyl protein motifs. The main focus of this paper is the large immunophilins FKBP51 and FKBP52, but other PPIases such as cyclophilin A and Pin1 are also described. From the hypothesis, it follows that the PPIase activity of these proteins might be less relevant, if at all, than the organization of protein complexes through versatile protein binding. Also see the video abstract here https://youtu.be/A33la0dx5LE .     

A novel myotropic peptide from the skin secretions of the tree frog, Polypedates pingbianensis

A novel myotropic peptide, polypedatein, was purified and characterized from the skin secretions of the tree frog, Polypedates pingbianensis. Its primary structure, TLLCKYFAIC, was determined by Edman degradation and mass spectrometry. Polypedatein was subjected to bioassays including myotropic, antimicrobial, and serine protease inhibitory activities, which are related with many amphibian skin bioactive peptides. It was found to elicit concentration-dependent contractile effects on isolated rat ileum. cDNA clones encoding the precursor of polypedatein were isolated by screening a skin cDNA library of P. pingbianensis and then sequenced. The amino acid sequence deduced from the cDNA sequences matches well with the result from Edman degradation. BLAST search revealed that the sequence of polypedatein did not show similarity to known protein or peptide sequences. Especially, polypedatein does not contain conserved structural motifs of other amphibian myotropic peptides, such as bradykinins, bombesins, cholecystokinin (CCK), and tachykinins, indicating that polypedatein belongs to a novel amphibian myotropic peptide family. The signal peptide of the precursor encoding polypedatein shows significant sequence identity to that of other amphibian skin defensive peptides, such as antimicrobial peptides, bradykinins, lectins, and serine protease inhibitors, suggesting that polypedatein belongs to a novel amphibian myotropic peptide family. Polypedatein is also the first bioactive peptide from the genus of the frog, Polypedates.     

A novel Kazal-type trypsin inhibitor from the skin secretion of the Central American red-eyed leaf frog, Agalychnis callidryas

The chemical complexity of the defensive skin secretion of the red-eyed leaf frog, (Agalychnis callidryas), has not been elucidated in detail. During a systematic study of the skin secretion peptidomes of phyllomedusine frogs, we discovered a novel Kazal-type protein with potent trypsin inhibitory activity (Ki = 1.9 nM) that displays the highest degree of structural similarity with Kazal proteins from bony fishes. The protein was located in reverse-phase HPLC fractions following a screen of such for trypsin inhibition and subsequent partial Edman degradation of the peak active fraction derived the sequence: ATKPR-QYIVL-PRILRPV-GT. The molecular mass of the major component in this fraction was established by MALDI-TOF MS as 5893.09 Da. This partial sequence (assuming blank cycles to be Cys residues) was used to design a degenerate primer pool that was employed successfully in RACE-PCR to clone homologous precursor-encoding cDNA that encoded a mature Kazal protein of 52 amino acid residues with a computed molecular mass of 5892.82 Da. The protein was named A. callidryas Kazal trypsin inhibitor (ACKTI). BLAST analysis revealed that ACKTI contained a canonical Kazal motif (C-x(7)-C-x(6)-Y-x(3)-C-x(2,3)-C). This novel amphibian skin Kazal trypsin inhibitor adds to the spectrum of trypsin inhibitors of Kunitz- and Bowman Birk-type reported from this amphibian source.     

Bi-functional peptides with both trypsin-inhibitory and antimicrobial activities are frequent defensive molecules in Ranidae amphibian skins

Amphibian skins act as the first line against noxious aggression by microorganisms, parasites, and predators. Anti-microorganism activity is an important task of amphibian skins. A large amount of gene-encoded antimicrobial peptides (AMPs) has been identified from amphibian skins. Only a few of small protease inhibitors have been found in amphibian skins. From skin secretions of 5 species (Odorrana livida, Hylarana nigrovittata, Limnonectes kuhlii, Odorrana grahami, and Amolops loloensis) of Ranidae frogs, 16 small serine protease inhibitor peptides have been purified and characterized. They have lengths of 17-20 amino acid residues (aa). All of them are encoded by precursors with length of 65-70 aa. These small peptides show strong trypsin-inhibitory abilities. Some of them can exert antimicrobial activities. They share the conserved GCWTKSXXPKPC fragment in their primary structures, suggesting they belong to the same families of peptide. Signal peptides of precursors encoding these serine protease inhibitors share obvious sequence similarity with those of precursors encoding AMPs from Ranidae frogs. The current results suggest that these small serine protease inhibitors are the common defensive compounds in frog skin of Ranidae as amphibian skin AMPs.     

Pachymedusa dacnicolor tryptophyllin-1: structural characterization, pharmacological activity and cloning of precursor cDNA

Tryptophyllins are a heterogenous group of amphibian skin peptides originally identified in skin extracts of Neotropical leaf frogs, Phyllomedusa sp., by chemical means. Until now, biosynthetic precursor structure and biological activity remain unreported. Here we describe the isolation of a novel, post-translationally modified tryptophyllin, Lys-Pro-Hyp-Ala-Trp-Val-Pro.amide (PdT-1), from the skin secretion of the Mexican leaf frog, Pachymedusa dacnicolor. Using a 3'- and 5'-RACE strategy and an in vitro skin cDNA library, the PdT-1-encoding precursor was cloned and found to consist of an open-reading frame of 62 amino acids with a single copy of PdT-1 located towards the C-terminus. A synthetic replicate of PdT-1 was found to be a potent myoactive agent, relaxing mammalian arterial smooth muscle and contracting small intestinal smooth muscle at nanomolar concentrations. PdT-1 is thus the first amphibian skin tryptophyllin to be pharmacologically characterized and the first whose precursor cDNA has been cloned.     

Changes in the activity of the maturation-promoting factor during meiotic maturation and following activation of amphibian and starfish oocytes: their correlations with protein phosphorylation

Changes in the extent of protein phosphorylation and their possible correlation with changes in the activity of maturation-promoting (MPF) factor were investigated throughout meiotic maturation and following activation of amphibian and starfish oocytes. Despite several exceptions in the pattern of phosphorylation of individual proteins, high and low levels of protein phosphorylation were found to be correlated with high and low levels of MPF activity. Both the extent of protein phosphorylation and MPF activity were found to drop upon parthenogenetic activation and to cycle synchronously thereafter in the amphibian. In contrast no drop in MPF activity or in the extent of protein phosphorylation was observed following activation of starfish oocytes with ionophore A23187. This suggests that changes of protein phosphorylation and of MPF activity are rather related to the progression of the cell cycle than directly to Ca2+-dependent activation reaction. In amphibians global protein kinase activity in homogenates was found to drop with MPF activity following activation. Changes in the ratio of threonine vs serine phosphorylation were also investigated during the course of meiotic maturation and activation in both amphibian and starfish oocytes: changes in the activity of MPF were found to be better correlated with changes in threonine than serine phosphorylation.     

Evolution of allantoinase and allantoicase involved in urate degradation in liver peroxisomes. A rapid purification of amphibian allantoinase and allantoicase complex, its subunit locations of the two enzymes, and its comparison with fish allantoinase and allantoicase

Allantoinase and allantoicase are located in the same protein molecule in amphibian liver, whereas the two enzymes are different proteins in marine fish and invertebrate liver (Takada, Y., and Noguchi, T. (1983) J. Biol. Chem. 258, 4762-4764). The amphibian enzyme was rapidly purified from frog liver by using its following characteristics. 1) The enzyme binds to the intracellular membranes in the hypotonic solution. 2) The membrane-bound enzyme is not solubilized by the detergent. 3) The membrane-bound enzyme is solubilized by oxaloacetate. The electrophoresis of the purified enzyme gave a single protein band in the absence of sodium dodecyl sulfate, and gave two protein bands with molecular weights of 48,000 and 54,000, respectively, in the presence of sodium dodecyl sulfate. With a specific antibody raised against each subunit, allantoinase activity was found to be from the large subunit, and allantoicase activity to be from the small subunit. This amphibian allantoinase and allantoicase complex was compared with allantoinase and allantoicase purified from fish liver. Fish allantoinase was a single peptide and fish allantoicase was composed of two identical subunits. Fish allantoinase had an identical molecular weight with amphibian large (allantoinase) subunit and the subunit of fish allantoicase with amphibian small (allantoicase) subunit. These results suggest that the evolution of fish to amphibian resulted in the dissociation of allantoicase into subunits and in the association of allantoinase with allantoicase. The two enzymes are lost by further evolution.     

非洲菊亲环素家族基因GCyP的克隆与生物信息学分析

亲环素(Cyclophilins,CyPs)具有肽脯氨酰顺反异构酶活性,催化蛋白质折叠过程,并且起着分子伴侣的作用,同时参与mRNA加工和信号转导等生物学过程.本研究在抑制性消减杂交获得表达序列标签(EST)的基础上,通过生物信息学方法获得了非洲菊亲环素家族基因GCyP的cDNA.进而设计特异引物,以非洲菊舌状花为材料,通过RT-PCR扩增并经T-A克隆后测序,获得一条长度为732 bp的序列.该序列经生物信息学分析确认其为GCyP,编码的GCyP含172个氨基酸残基,属于单结构域胞质型亲环素.GCyP序列提交GenBank后接收,登录号为EU1269167.     

Isolation and cDNA cloning of cholecystokinin from the skin of Rana nigrovittata

Many neuroendocrine peptides that are distributed in amphibian gastrointestinal tract and central nervous system are also found in amphibian skins, and these peptides are classified into skin-gut-brain triangle peptides, such as bombesins, gastrin-releasing peptides. Cholecystokinins (CCKs) are neuroendocrine peptides known for their production in the gastrointestinal tract and central nervous system of mammalians. Several CCKs have been identified from two amphibians, Rana catesbeiana and Xenopus laevis. These amphibian CCKs are found to be express in brain and in the gastrointestinal tract, but not in skin. In the current report, a cholecystokinin (CCK) isoform was identified from skin secretions of the frog, Rana nigrovittata. Its amino acid sequence is RVDGNSDQKAVIGAMLAKDLQTRKAGSSTGRYAVLPNR PVIDPTHRINDRDYMGWMDF, which is the same with that of CCK from R. catesbeiana. Four different cDNAs (GenBank accession nos. EF608063-6) encoding CCK precursors were cloned from the cDNA library of the skin of R. nigrovittata. The present data demonstrated that amphibian CCK could also be expressed in gastrointestinal tract, central nervous system and skin as other amphibian skin-gut-brain triangle peptides.     

Germ Tube Mediated Invasion of Batrachochytrium dendrobatidis in Amphibian Skin Is Host Dependent

Batrachochytrium dendrobatidis (Bd) is the causative agent of chytridiomycosis, a fungal skin disease in amphibians and driver of worldwide amphibian declines.We focussed on the early stages of infection by Bd in 3 amphibian species with a differential susceptibility to chytridiomycosis. Skin explants of Alytes muletensis, Litoria caerulea and Xenopus leavis were exposed to Bd in an Ussing chamber for 3 to 5 days. Early interactions of Bd with amphibian skin were observed using light microscopy and transmission electron microscopy. To validate the observations in vitro, comparison was made with skin from experimentally infected frogs. Additional in vitro experiments were performed to elucidate the process of intracellular colonization in L. caerulea.Early interactions of Bd with amphibian skin are: attachment of zoospores to host skin, zoospore germination, germ tube development, penetration into skin cells, invasive growth in the host skin, resulting in the loss of host cell cytoplasm. Inoculation of A. muletensis and L. caerulea skin was followed within 24 h by endobiotic development, with sporangia located intracellularly in the skin. Evidence is provided of how intracellular colonization is established and how colonization by Bd proceeds to deeper skin layers. Older thalli develop rhizoid-like structures that spread to deeper skin layers, form a swelling inside the host cell to finally give rise to a new thallus.In X. laevis, interaction of Bd with skin was limited to an epibiotic state, with sporangia developing upon the skin. Only the superficial epidermis was affected. Epidermal cells seemed to be used as a nutrient source without development of intracellular thalli. The in vitro data agreed with the results obtained after experimental infection of the studied frog species. These data suggest that the colonization strategy of B. dendrobatidis is host dependent, with the extent of colonization most likely determined by inherent characteristics of the host epidermis.     

A Large Intrinsically Disordered Region in SKIP and Its Disorder-Order Transition Induced by PPIL1 Binding Revealed by NMR

Intrinsically disordered proteins or protein regions play an important role in fundamental biological processes. During spliceosome activation, a large structural rearrangement occurs. The Prp19 complex and related factors are involved in the catalytic activation of the spliceosome. Recent mass spectrometric analyses have shown that Ski interaction protein (SKIP) and peptidylprolyl isomerase-like protein 1 (PPIL1) are Prp19-related factors that constitute the spliceosome B, B*, and C complexes. Here, we report that a highly flexible region of SKIP (SKIPN, residues 59–129) is intrinsically disordered. Upon binding to PPIL1, SKIPN undergoes a disorder-order transition. A highly conserved fragment of SKIP (residues 59–79) called the PPIL1-binding fragment (PBF) was sufficient to bind PPIL1. The structure of PBF·PPIL1 complex, solved by NMR, shows that PBF exhibits an ordered structure and interacts with PPIL1 through electrostatic and hydrophobic interactions. Three subfragments in the PBF (residues 59–67, 68–73, and 74–79) show hook-like backbone structure, and interactions between these subfragments are necessary for PBF·PPIL1 complex formation. PPIL1 is a cyclophilin family protein. It is recruited by SKIP into the spliceosome by a region other than the peptidylprolyl isomerase active site. This enables the active site of PPIL1 to remain open in the complex and still function as a peptidylprolyl cis/trans-isomerase or molecular chaperon to facilitate the folding of other proteins in the spliceosomes. The large disordered region in SKIP provides an interaction platform. Its disorder-order transition, induced by PPIL1 binding, may adapt the requirement for a large structural rearrangement occurred in the activation of spliceosome.     

Dermatoxin and phylloxin from the waxy monkey frog, Phyllomedusa sauvagei: cloning of precursor cDNAs and structural characterization from lyophilized skin secretion

Amphibian skin is a morphologically, biochemically and physiologically complex organ that performs the wide range of functions necessary for amphibian survival. Here we describe the primary structures of representatives of two novel classes of amphibian skin antimicrobials, dermatoxin and phylloxin, from the skin secretion of Phyllomedusa sauvagei, deduced from their respective precursor encoding cDNAs cloned from a lyophilized skin secretion library. A degenerate primer, designed to a highly conserved domain in the 5'-untranslated region of analogous peptide precursor cDNAs from Phyllomedusa bicolor, was employed in a 3'-RACE reaction. Peptides with molecular masses coincident with precursor-deduced mature toxin peptides were identified in LC/MS fractions of skin secretion and primary structures were confirmed by MS/MS fragmentation. This integrated experimental approach can thus rapidly expedite the primary structural characterization of amphibian skin peptides in a manner that circumvents specimen sacrifice whilst preserving robustness of scientific data.     

Interaction of the periplasmic peptidylprolyl cis-trans isomerase SurA with model peptides. The N-terminal region of SurA id essential and sufficient for peptide binding

One of the rate-limiting steps in protein folding has been shown to be the cis-trans isomerization of proline residues, which is catalyzed by a range of peptidylprolyl cis-trans isomerases. To characterize the interaction between model peptides and the periplasmic peptidylprolyl cis-trans isomerase SurA from E. coli, we employed a chemical cross-linking strategy that has been used previously to elucidate the interaction of substrates with other folding catalysts. The interaction between purified SurA and model peptides was significant in that it showed saturation and was abolished by denaturation of SurA; however the interaction was independent of the presence of proline residues in the model peptides. From results obtained by limited proteolysis we conclude that an N-terminal fragment of SurA, comprising 150 amino acids that do not contain the active sites involved in the peptidylprolyl cis-trans isomerization, is essential for the binding of peptides by SurA. This was confirmed by probing the interaction of the model peptide with the recombinant N-terminal fragment, expressed in Escherichia coli. Hence we propose that, similar to protein disulfide isomerase and other folding catalysts, SurA exhibits a modular architecture composed of a substrate binding domain and distinct catalytically active domains.     

Purification of a lysozyme from skin secretions of Bufo andrewsi

A novel toad lysozyme (named BA-lysozyme) was purified from skin secretions of Bufo andrewsi by a three-step chromatography procedure. BA-lysozyme is a single chain protein and the apparent molecular weight is about 15 kDa as judged by SDS-PAGE. The specific lytic activity against Micrococcus lysodeikticus of BA-lysozyme is 2.7 x 10(5) units/mg, indicating that it is a potent lysozyme. It displayed potent bactericidal activity against Staphylococcus aureus and Escherichia coli with minimal inhibitory concentrations (MIC) of 1 and 8 microM, respectively. The deduced primary structure of BA-lysozyme from cloned cDNA was confirmed by N-terminal sequencing and peptide mass fingerprinting. Its amino acid sequence shares 56.5% identity with that of chicken egg-white lysozyme. Phylogenetic analysis indicates that B. andrewsi lysozyme is closely related to that of turtle. This is the first report on the isolation and primary structure determination of amphibian lysozyme.     

Biochemical Analyses of Proteins from <Emphasis Type="Italic">Duttaphrynus melanostictus</Emphasis> (<Emphasis Type="Italic">Bufo melanostictus</Emphasis>) Skin Secretion: Soluble Protein Retrieval from a Viscous Matrix by Ion-Exchange Batch Sample Preparation

A crucial step in scientific analysis can be sample preparation, and its importance increases in the same rate as the sensitivity of the following employed/desired analytical technique does. The need to analyze complex, viscous matrices is not new, and diverse approaches have been employed, with different success rates depending on the intended molecules. Solid-phase extraction, for example, has been successfully used in sample preparation for organic molecules and peptides. However, due to the usual methodological conditions, biologically active proteins are not successfully retrieved by this technique, resulting in a low rate of protein identification reported for the viscous amphibian skin secretion. Here we describe an ion-exchange batch processing sample preparation technique that allows viscous or adhesive materials (as some amphibian skin secretions) to be further processed by classical liquid chromatography approaches. According to our protocol, samples were allowed to equilibrate with a specific resin that was washed with appropriated buffers in order to yield the soluble protein fraction. In order to show the efficiency of our methodology, we have compared our results to classically prepared skin secretion, i.e., by means of filtration and centrifugation. After batch sample preparation, we were able to obtain reproductive resolved protein chromatographic profiles, as revealed by SDS-PAGE, and retrieve some biological activities, namely, hydrolases belonging to serine peptidase family. Not only that, but also the unbound fraction was rich in low molecular mass molecules, such as alkaloids and steroids, making this sample preparation technique also suitable for the enrichment of such molecules.     

Targeting of frog prodermorphin to the regulated secretory pathway by fusion to proenkephalin

We have investigated the sorting and processing of the amphibian precursor prepro-dermorphin in mammalian cells. Dermorphin, a D-alanine-containing peptide with potent opioid activity, has been isolated from the skin of the frog Phyllomedusa sauvagei. The maturation of this peptide from the precursor involves several posttranslational steps. Recombinant vaccinia viruses were used to infect AtT-20, PC12, and HeLa cells to study the sorting and processing of prepro-dermorphin. While this precursor was not processed in any of the examined cell lines, AtT-20 cells were able to process approximately 40% of a chimeric precursor consisting of the first 241 amino acids of prepro-enkephalin fused to a carboxy-terminal part of pro-dermorphin. By immunogold-EM, we could show that the chimeric protein, but not pro-dermorphin, was sorted to dense-core secretion granules. The processing products could be released upon stimulation by 8-Br-cAMP. We conclude that the pro-enkephalin part of the fusion protein contains the information for targeting to the regulated pathway of secretion, while this sorting information is missing in pro-dermorphin. This indicates that sorting mechanisms may differ between amphibian and mammalian cells.     

Identification and partial characterization of an elastolytic protease in the amphibian pathogen Batrachochytrium dendrobatidis

Batrachochytrium dendrobatidis (Bd) is a fungus that causes chytridiomycosis, a disease that has been implicated as a cause of amphibian population declines worldwide. Infected animals experience hyperkeratosis and sloughing of the epidermis due to penetration of the keratinized tissues by the fungus. These symptoms have led us to postulate that Bd produces proteases that play a role in the infection process. Here, we show that Bd is capable of degrading elastin in vitro, a protein found in the extracellular matrix of the host animal. Elastolytic enzyme activity was partially purified using ion exchange chromatography and size-exclusion filtration from cultures grown in inducing media. The elastolytic activity of the purified fraction had a pH optimum of 8, was strongly inhibited by EDTA and phenylmethylsulfonyl fluoride (PMSF), and was partially inhibited by an elastase-specific inhibitor. This activity was also enhanced by the presence of Mg2+ and Ca2+ but not Zn2+. An antiserum directed against Aspergillus fumigatus serine protease (Alp) was found to react with a polypeptide of approximately 110 kDa from the purified material. Using immunofluorescence, this antiserum was also observed to react with zoospores and sporangia grown on toad skin. These observations suggest that Bd may produce proteases similar to those produced by other pathogenic fungi that are capable of degrading proteins found in the extracellular matrix. The proteolytic activity exhibited in vitro might aid the organism in its ability to colonize and destroy the epidermis of its amphibian host.     

Hainanenins: a novel family of antimicrobial peptides with strong activity from Hainan cascade-frog, Amolops hainanensis

Antimicrobial peptides (AMPs) secreted by amphibian skin represent an important innate immune defense strategy. There are more than 340 species in the family of Ranidae worldwidely, and from which nearly 100 families of AMPs comprising between 8 and 48 amino acid (aa) residues have been characterized. In current work, two novel AMPs were purified from the skin secretion of Hainan cascade-frog, Amolops hainanensis, and 31 cDNA sequences encoding 10 novel AMPs belonging to 4 families were cloned from the constructed skin cDNA library of A. hainanensis. Among these 10 AMPs, 5 peptides represent the prototypes of a novel amphibian AMP family. According to the generic name of the species of origin, they were designated as hainanenin-1-5. Each of them consists of 21 aa residues with a C-terminal disulphide loop of 7 residues between Cys(15) and Cys(21). Two of them (hainanenin-1 and 5) were then synthesized and their in vitro activities were screened, including antimicrobial, hemolytic and antioxidant activities. The results showed that hainanenin-1 and 5 possessed strong and broad-spectrum antimicrobial activities against Gram-positive, Gram-negative bacteria and fungi, including a large number of clinically isolated drug-resistant pathogenic microorganisms, and slight antioxidant activity. Undesirably, hainanenin-1 and 5 exhibited strong hemolytic activity on human erythrocytes. The discovery of hainanenins and their great antimicrobial potency provides new templates for anti-infective agent design.     

The Amphibian Melanization Inhibiting Factor (MIF) Blocks the α-MSH Effect on Mouse Malignant Melanocytes

We have found that a melanization inhibitory factor (MIF) extracted from the ventral skin of Rana forreri has a slight inhibitory effect on the activity levels of tyrosinase and dopachrome tautomerase in B16/F10 and Cloudman S-91 murine melanoma cell lines. Furthermore, this factor appears to block the effects of α-MSH on these enzymatic activities. However, MIF treatment does not affect the melanogenic action of theophylline on the same cells, suggesting that MIF acts proximal to MSH-mediated cAMP formation, possibly by interaction with the MSH receptor. In this way, we show that this amphibian factor has biological activity on mammalian melanocytes. This suggests the existence of mammalian counterparts of amphibian MIF in the mouse integument that might regulate epidermal melanocytes. These peptides might be related to the agouti protein, as they share similar mechanisms of action. The interaction of different peptides with the MSH receptor would be a complex but general mechanism responsible for many mammalian coat color variants.     

Requirement of a mip-like gene for virulence in the phytopathogenic bacterium Xanthomonas campestris pv. campestris

Macrophage infectivity potentiators (Mips) are FKBP domain-containing proteins reported as virulence factors in several human pathogens, such as members of genera Legionella, Salmonella and Chlamydia. The putative peptidylprolyl cis-trans isomerase (PPIase) encoded by XC2699 of the plant bacterial pathogen Xanthomonas campestris pv. campestris 8004 exhibits a 49% similarity at the amino-acid level to the Mip protein of Legionella pneumophila. This mip-like gene, XC2699, was overexpressed in Escherichia coli and the purified (His)6-tagged Mip-like protein encoded by XC2699 exhibited a PPIase activity specifically inhibited by FK-506. A mutation in the mip-like gene XC2699 led to significant reductions in virulence and replication capacity in the host plant Chinese radish (Raphanus sativus L. var. radiculus Pers.). Furthermore, the production of exopolysaccharide and the activity of extracellular proteases, virulence factors of X. campestris pv. campestris, were significantly decreased in the mip-like mutant. These results reveal that the mip-like gene is involved in the pathogenesis of X. campestris pv. campestris through an effect on the production of these virulence factors.