Cloning and Characterization of the Gene Encoding for OMP-PD Porin: The Major <Emphasis Type="Italic">Photobacterium damsela</Emphasis> Outer Membrane Protein

The outer membrane protein of Photobacterium damsela (OMP-PD) and the gene encoding for this porin protein were isolated and characterized. The deduced amino acid sequence of the OMP-PD monomer has 338 amino acids and a calculated molecular weight of 36,951 Da. This sequence includes a 22-amino acid signal peptide at the N-terminal, which is not found when the monomer is located in the outer membrane. Native OMP-PD protein forms a trimeric structure of approximately 110 kDa. It exhibits resistance to proteases, and it can be cleaved only following denaturation by SDS. The degree of identity of the OMP-PD amino acid sequence to porins from the Enterobacteriaceae was only 24%. Identity to Vibrio or Photobacterium porins was 38% and 48%, respectively. Nevertheless, the multiple alignment of this sequence with other structurally defined Enterobacteria porins demonstrated that the location of the 16 beta-strands and eight external loops, including a larger external L3 loop, are conserved in OMP-PD. These results, together with the previously known ability of OMP-PD to form an ion channel in artificial liposomes, strongly support its role as a porin in P. damsela and will help further investigations into the role of OMP-PD in P. damsela pathogenicity.     

Nucleotide and derived amino acid sequences of the major porin of Comamonas acidovorans and comparison of porin primary structures.

The DNA sequence of the gene which codes for the major outer membrane porin (Omp32) of Comamonas acidovorans has been determined. The structural gene encodes a precursor consisting of 351 amino acid residues with a signal peptide of 19 amino acid residues. Comparisons with amino acid sequences of outer membrane proteins and porins from several other members of the class Proteobacteria and of the Chlamydia trachomatis porin and the Neurospora crassa mitochondrial porin revealed a motif of eight regions of local homology. The results of this analysis are discussed with regard to common structural features of porins.     

Diffusion of beta-lactam antibiotics through oligomeric or monomeric porin channels of some gram-negative bacteria

The penetration of anionic beta-lactam antibiotics through porins was evaluated as a mechanism of drug resistance. The major proteins with porin activity were purified from the outer membranes of six bacteria. Three of the six porins were oligomeric porins. The molecular weights of their monomers were 37 kDa from Photobacterium damsela, 42 kDa from Serratia liquefaciens, and 36 kDa from E. coli B. The other three porins were heat-modifiable monomeric porins with molecular weights of 43 kDa from Porphyromonas asaccharolytica and Acinetobacter baumannii, and 37 kDa from Escherichia coli K12.Comparison of the six porin proteins revealed that, independent of their aggregation state, their amino acid content is similar but not identical. All have double the amount of negatively charged amino acids compared with positively charged amino acids. They have a similar polarity and polarity index. Two of the six tested bacteria do not produce beta-lactamase. These two bacteria were sensitive to the different beta-lactams tested. The other four bacteria were resistant to all or to several beta-lactams.A modified liposome swelling method was used for determining the rate of penetration of charged beta-lactam antibiotics. Zwitterionic beta-lactams were found to penetrate into liposomes at a rate that more or less fits their molecular weight, whether the porins are monomeric or oligomeric. The penetration rates of negatively charged beta-lactams are different for oligomeric and monomeric porins. Negatively charged beta-lactams penetrate through oligomeric porins better than estimated by their molecular weight, whereas monomeric porins are less penetrable to negatively charged beta-lactams than estimated by their molecular weight. The contribution of all types of porins to the susceptibility of bacteria to beta-lactam antibiotics (zwitterionic or negatively charged) is apparently doubtful. The porins may decrease or increase bacterial penetration rates to beta-lactams, and only the existence of a potential beta-lactamase that can destroy the penetrating drug will cause resistance.     

Diffusion of β-Lactam Antibiotics Through Oligomeric or Monomeric Porin Channels of Some Gram-Negative Bacteria

The penetration of anionic β-lactam antibiotics through porins was evaluated as a mechanism of drug resistance. The major proteins with porin activity were purified from the outer membranes of six bacteria. Three of the six porins were oligomeric porins. The molecular weights of their monomers were 37 kDa from Photobacterium damsela, 42 kDa from Serratia liquefaciens, and 36 kDa from E. coli B. The other three porins were heat-modifiable monomeric porins with molecular weights of 43 kDa from Porphyromonas asaccharolytica and Acinetobacter baumannii, and 37 kDa from Escherichia coli K12. Comparison of the six porin proteins revealed that, independent of their aggregation state, their amino acid content is similar but not identical. All have double the amount of negatively charged amino acids compared with positively charged amino acids. They have a similar polarity and polarity index. Two of the six tested bacteria do not produce β-lactamase. These two bacteria were sensitive to the different β-lactams tested. The other four bacteria were resistant to all or to several β-lactams. A modified liposome swelling method was used for determining the rate of penetration of charged β-lactam antibiotics. Zwitterionic β-lactams were found to penetrate into liposomes at a rate that more or less fits their molecular weight, whether the porins are monomeric or oligomeric. The penetration rates of negatively charged β-lactams are different for oligomeric and monomeric porins. Negatively charged β-lactams penetrate through oligomeric porins better than estimated by their molecular weight, whereas monomeric porins are less penetrable to negatively charged β-lactams than estimated by their molecular weight. The contribution of all types of porins to the susceptibility of bacteria to β-lactam antibiotics (zwitterionic or negatively charged) is apparently doubtful. The porins may decrease or increase bacterial penetration rates to β-lactams, and only the existence of a potential β-lactamase that can destroy the penetrating drug will cause resistance. Received: 28 January 2002 / Accepted: 4 May 2002     

Characterization of Porins Isolated from the Outer Membrane of Serratia liquefaciens

A major outer membrane protein with an apparent molecular weight of 42 kDa was purified from Serratia liquefaciens grown on Brain Heart Infusion medium. The same protein was obtained when the cells were grown on a synthetic medium supplemented with 2% glucose. The amino acid composition of this protein revealed it to be hydrophilic. The pore-forming ability of the 42-kDa protein was determined by the liposome swelling assay. This assay demonstrated that the protein forms nonspecific channels with a diameter between 1.16 and 1.6 nm. An additional protein with a molecular weight of 47 kDa was obtained on synthetic medium supplemented with maltose. This protein exhibited specific pore-forming ability to maltose and maltodextrins, but was also permeable to other compounds, according to their size. When bacteria were grown on Nutrient Broth medium, two outer membrane proteins with molecular weights of 41 kDa and 42 kDa were produced by the bacteria. All three types of proteins represent monomers of respective oligomers. The monomers did not exhibit pore-forming ability when incorporated into liposomes. We, therefore, propose that the oligomer is the functional unit of a porin capable of forming permeability channels in the outer membrane of Serratia liquefaciens. These results indicate that S. liquefaciens contains several porins exhibiting specific osmoregulation or that are induced by a specific nutrient, where the 42-kDa outer membrane protein of this bacterium is certainly a major porin. Received: 6 July 1998 / Accepted: 19 August 1998     

Isolation and characterization of porins from <Emphasis Type="Italic">Desulfovibrio piger</Emphasis> and <Emphasis Type="Italic">Bilophila wadsworthia</Emphasis>: structure and gene sequencing

The outer membrane proteins of Desulfovibrio piger and Bilophila wadsworthia (Omp-DP and Omp-BW, respectively) and the genes encoding them (omp-DP and omp-BW) were isolated and characterized. Native Omp-DP and Omp-BW form a trimeric structure of approximately 120 kDa. These proteins disaggregated into monomers with a molecular weight of approximately 53 kDa after heating at 95°C for 10 min. The pore-forming abilities of these oligomeric proteins demonstrated that they form small nonspecific channels with an exclusion limit of 260–300 Da. The omp-DP and omp-BW genes were cloned and sequenced. Sequence analyses revealed an open reading frame of 1,512 bp for omp-DP and 1,440 bp for omp-BW. The mature Omp-DP protein consisted of 480 amino acids and had a calculated MW of 53,290 Da. The mature Omp-BW protein consisted of 456 amino acids and had a calculated MW of 50.050 Da. Alignment of Omp-DP with Omp-BW revealed 54% homology, whereas alignment with other known porins showed a low level of homology. Analysis of the secondary structures indicated that both proteins span the outer membrane 18 times with amphipathic β-strands. This research presents porins which were isolated and characterized for the first time from bacteria belonging to the Desulfovibrionaceae family. O. Avidan and E. Kaltageser have contributed equally to this work.     

Colicin pore-forming domains bind to Escherichia coli trimeric porins

Colicin N kills sensitive Escherichia coli cells by first binding to its trimeric receptor (OmpF) via its receptor binding domain. It then uses OmpF to translocate across the outer membrane and in the process it also needs domains II and III of the protein TolA. Recent studies have demonstrated sodium dodecyl sulfate- (SDS) dependent complex formation between trimeric porins and TolA-II. Here we demonstrate that colicin N forms similar complexes with the same trimeric porins and that this association is unexpectedly solely dependent upon the pore-forming domain (P-domain). No binding was seen with the monomeric porin OmpA. In mixtures of P-domain and TolA with OmpF porin, only binary and no ternary complexes were observed, suggesting that binding of these proteins to the porin is mutually exclusive. Pull-down assays in solution show that porin-P-domain complexes also form in the presence of outer membrane lipopolysaccharide. This indicates that an additional colicin-porin interaction may occur within the outer membrane, one that involves the colicin pore domain rather than the receptor-binding domain. This may help to explain the role of porins and TolA-II in the later stages of colicin translocation.     

<Emphasis Type="Italic">Yersinia pseudotuberculosis</Emphasis> mutant OmpF porins with deletions of the external loops: genetic constructions design,expression, isolation and refolding

Yersinia pseudotuberculosis outer membrane (OM) recombinant mutant OmpF porins with deletions of the external loops L1, L6 and L8 were obtained using site-directed mutagenesis of the recombinant plasmid including ompF gene. Heterologeous expression of the mutant proteins was carried out in strain Rosetta of Escherichia coli (Novagen, USA), porins with the deletions were isolated from the inclusion bodies. Oligomers of mutant porins were obtained as result of dialysis and ion-exchange chromatography. Spatial structure of the mutant proteins was found to have special features in comparison with that of the full-structured OmpF porin on the level of both secondary and tertiary structure. As shown using bilayer lipid membrane (BLM) technique the absence of the loops L1, L6 and L8 didn’t affect the conductivity level of Y. pseudotuberculosis porin channel. The absence of the loops mentioned above has a significant influence on the antigenic structure of the mutant porins as demonstrated using immunoblotting technique and ELISA.     

The porins from the halophilic species Ectothiorhodospira shaposhnikovii and Ectothiorhodospira vacuolata

Major outer membrane proteins with porin activity were isolated from cell envelopes of the halophilic strains Ectothiorhodospira shaposhnikovii N1 and Ectothiorhodospira vacuolataβ1. The porins were obtained as oligomers. They dissociated into monomers by heat or EDTA treatment. The molecular masses of the monomers were determined by mass spectrometry to be 39,285 and 37,160 Da for E. shaposhnikovii N1 and E. vacuolataβ1, respectively. Both were shown by analytical ultracentrifugation to be trimers of about 112,000 Da. Circular dichroism spectra indicated predominantly β-sheet structure. The 18 N-terminal amino acid sequences of the two porins were identical except for the amino acids in positions 12 and 14. No sequence similarity with the primary structure of known porins was found. In reconstitution experiments with lipid bilayers, the porins of E. shaposhnikovii N1 and E. vacuolataβ1 formed channels with a single-channel conductance of 1.5 and 0.7 nS, respectively, in 1 M KCl. The single-channel conductance saturated with increasing salt concentration, indicating a putative binding-site for anions in the channel since both porins exhibited anion-selectivity. For the porin of E. vacuolataβ1, but not for that of E. shaposhnikovii N1, an influence of detergent concentration on the single-channel conductance was observed. Received: 3 April 1996 / Accepted: 31 May 1996     

The periplasmic molecular chaperone protein SurA binds a peptide motif that is characteristic of integral outer membrane proteins

The Escherichia coli SurA protein is a periplasmic molecular chaperone that facilitates correct folding of outer membrane porins. The peptide binding specificity of SurA has been characterized using phage display of heptameric peptides of random sequence. The consensus binding pattern of aromatic-polar-aromatic-nonpolar-proline amino acids emerges for both SurA and a SurA "core domain," which remains after deletion of a peripheral peptidyl-proline isomerase domain. Isothermal titration calorimetry with a high affinity heptameric peptide of sequence WEYIPNV yields peptide affinities in the range of 1-14 microm for both SurA and its core domain. Although the peptide consensus aromatic-polar-aromatic-nonpolar-proline occurs infrequently in E. coli proteins, the less restrictive tripeptide motif aromatic-random-aromatic appears with greater-than-random frequency in outer membrane proteins and is prevalent in the "aromatic bands" of the porin beta barrel structures. Thus, SurA recognizes a peptide motif that is characteristic of integral outer membrane proteins.     

Isolation and characterization of OmpF-like porin from <Emphasis Type="Italic">Yersinia ruckeri</Emphasis>

The polypeptide profile of the porin protein fraction of Yersinia ruckeri, a Gram-negative bacterium causing yersiniosis in fish, has been shown to depend on cultivation temperature. OmpF-like porins are expressed mainly in the outer membrane (OM) of the “cold” variant (4°C) of the microorganism and OmpC-like proteins are expressed in the OM of the “warm” variant (37°C). Both types of porins are present in the OM of Y. ruckeri at room temperature. The OmpF-like porin of the “cold” variant was isolated and characterized. The molecular weight and primary structure of the protein were determined. The methods of optical spectroscopy (circular dichroism and intrinsic protein fluorescence) have shown that the protein has a spatial structure typical of β-structured porins from the OM of Gram-negative bacteria. The functional activity of isolated protein was characterized by the bilayer lipid membrane (BLM) technique. The most probable level of channel conductivity was 320 ± 60 pS, corresponding to the channel conductivity of OmpF porins of the genus Yersinia. The distinctive feature of OmpF porin from Y. ruckeri is high thermostability of its functionally active conformation: the protein forms stable pores in the BLM even after heating to 85°C.     

Purification, amino acid composition and N-terminal sequence of the major protein (protein H) of the outer membrane of Pasteurella multocida]

The major protein (protein H) of the outer membrane of Pasteurella multocida was purified by size-exclusion chromatography after selective extraction with detergents. The protein forms homotrimers which are stable in the presence of SDS at room temperature. Upon treatment at 100 degrees C, the protein is fully dissociated by the detergent into monomers exhibiting an apparent molecular mass of 37 kDa as estimated by electrophoresis. The amino acid composition of protein H is characterized by a low hydropathy index (HI = -0.40) and is strongly related to the compositions of bacterial porins, notably porins P2 (Haemophilus influenzae), PIA (Neisseria gonorrhoeae) and Cl.2 ("class 2 porin" of N. meningitidis). The N-terminal amino acid sequence of protein H shares a strong homology with those of porins OmpC (Escherichia coli) and P2. These data indicate that protein H of P. multocida is a porin belonging to the superfamily of the non-specific porins of Gram-negative eubacteria outer membrane.     

The TolB protein interacts with the porins of Escherichia coli.

TolB is a periplasmic protein of the cell envelope Tol complex. It is partially membrane associated through an interaction with the outer membrane lipoprotein PAL (peptidoglycan-associated lipoprotein), which also belongs to the Tol system. The interaction of TolB with outer membrane porins of Escherichia coli was investigated with a purified TolB derivative harboring a six-histidine tag. TolB interacted with the trimeric porins OmpF, OmpC, PhoE, and LamB but not with their denatured monomeric forms or OmpA. These interactions took place both in the presence and in the absence of lipopolysaccharide. TolA, an inner membrane component of the Tol system, also interacts with the trimeric porins via its central periplasmic domain (R. Dérouiche, M. Gavioli, H. Bénédetti, A. Prilipov, C. Lazdunski, and R. Lloubès, EMBO J. 15:6408-6415, 1996). In the presence of the purified central domain of TolA (TolAIIHis), the TolB-porin complexes disappeared to form TolAIIHis-porin complexes. These results suggest that the interactions of TolA and TolB with porins might take place in vivo and might be concomitant events participating in porin assembly. They also suggest that the Tol system as a whole may be involved in porin assembly in the outer membrane.     

Structure and function of pore-forming proteins from bacteria of the genus Yersinia: I. Isolation and a comparison of physicochemical properties and functional activity of Yersinia porins

The molecular organization and functional activity of porins isolated from the outer membrane (OM) of the Yersinia enterocolitica and three phylogenetically close nonpathogenic Yersinia species (Y. intermedia, Y. kristensenii, and Y. frederiksenii) cultured at 6–8°C were comparatively studied for the first time. The proteins were isolated in two molecular forms (trimeric and monomeric), and their spatial structures were characterized by the methods of optical spectroscopy, CD and intrinsic protein fluorescence. The studied porins were shown to belong to the β-structural proteins (they have 59–96% total β structures and 0–17% α helices). The spatial structures of the proteins were demonstrated to depend on the nature of the detergent used for solubilization. Unlike the enterobacterial pore-forming proteins, the porin trimers are less stable to sodium dodecyl sulfate (SDS). The spatial structures of the porins become more compact after the substitution of octyl β-D-glucoside for SDS: the content of β structures increases and the accessibility of Trp residues to solvent decreases. It was established with the use of the technique of bilayer lipid membranes that the functional properties of the porins are similar to those of the OmpF proteins of Gram-negative bacteria. Trimers are functionally active forms of the porins. Special features of the pore-forming activity of the Yersinia porins were revealed to depend on the microorganism species and the value of the membrane potential.     

High‐resolution architecture of the outer membrane of the Gram‐negative bacteria Roseobacter denitrificans

The outer membrane of Gram‐negative bacteria protects the cell against bactericidal substances. Passage of nutrients and waste is assured by outer membrane porins, beta‐barrel transmembrane channels. While atomic structures of several porins have been solved, so far little is known on the supramolecular structure of the outer membrane. Here we present the first high‐resolution view of a bacterial outer membrane gently purified maintaining remnants of peptidoglycan on the perisplasmic surface. Atomic force microscope images of outer membrane fragments of the size of ～50% of the bacterial envelope revealed that outer membrane porins are by far more densely packed than previously assumed. Indeed the outer membrane is a molecular sieve rather than a membrane. Porins cover ～70% of the membrane surface and form locally regular lattices. The potential role of exposed aromatic residues in the formation of the supramolecular assembly is discussed. Finally, we present first structural data of the outer membrane porin from the marine Gram‐negative bacteria Roseobacter denitrificans, and we perform a sequence alignment with porins of known structure.     

Porin Isolated from the Outer Membrane of <Emphasis Type="Italic">Erwinia amylovora</Emphasis> and Its Encoding Gene

A major Erwinia amylovora outer-membrane protein (Omp-EA) and the gene encoding for this protein (omp-EA) were isolated and characterized. The native Omp-EA protein forms a trimeric structure of approximately 114 kDa. This protein demonstrated high resistance to detergents such as SDS and octyl-glucopyranoside, but disaggregated to monomers with a molecular weight (MW) of approximately 39 kDa after heating at 95°C for 10 minutes in sample buffer. The pore-forming ability of the oligomeric Omp-EA was determined by the liposome swelling assay, demonstrating that the oligomeric protein formed nonspecific channels with an exclusion limit of approximately 660 Da. On dissociation, the monomers did not exhibit pore-forming ability. The omp-EA gene was cloned and sequenced (GenBank Accession No. DQ184680). Sequence analysis revealed an open reading frame of 1152 bases. The deduced amino-acid sequence had 383 amino acids. The mature protein consisted of 362 amino acids and had a calculated MW of 39,210 Da. Multiple-sequence alignment of Omp-EA with other porins from the Enterobacteriaceae family revealed 51% to 63% identity. The first 16 amino acids from the N-terminal exhibited the highest identity (100%) to the porins OmpC, OmpF, and PhoE of Escherichia coli. Two methods were used to predict the secondary structure: APSSP2 and Hidden and Markov’s model. The monomers of Omp-EA porin presented a topology of 16 transmembranal β-strands. The area of the loops between the β -strands was proposed. It is suggested that further research on the porin and its loops may be important for understanding the mechanism of E. amylovor to invade plant tissues.     

TolA central domain interacts with Escherichia coli porins.

TolA is an inner membrane protein with three domains: a transmembrane N-terminus and periplasmic central and C-terminal domains. The interaction of TolA with outer membrane porins of Escherichia coli was investigated. Western blot analyses of cell extracts with anti-TolA antibodies indicated that TolA forms high molecular weight complexes specifically with trimeric OmpF, OmpC, PhoE and LamB, but not with OmpA. The interaction of purified TolA domains with purified porins was also studied. TolA interacted with OmpF, PhoE and LamB porins via its central domain, but not with either their denatured monomeric forms or OmpA. Moreover, the presence or absence of lipopolysaccharides associated with trimeric porins did not modify the interactions. These results suggest that the specific interaction of TolA with outer membrane porins might be relevant to the function of Tol proteins.     

Identification of human porins. II. Characterization and primary structure of a 31-lDa porin from human B lymphocytes (Porin 31HL)

We characterize and describe for the first time the primary structure of a human porin with the molecular mass of 31 kDa derived from the plasmalemm of B-lymphocytes (Porin 31HL). Porin 31HL is shown to be a basic, channel forming membrane protein. The protein chain is composed of 282 amino acids with a relative molecular mass of 30641 Da without derivatisation. It is not a glycoprotein. The N-terminus is acetylated. Altogether the amino-acid sequence shows 56% hydrophilic or charged amino acids arranged in alternating regions of hydrophilic or hydrophobic character as it is typical for porins. In addition the 18 N-terminal amino acids of Porin 31HL can be arranged to an amphilic alpha-helix like in other porins. Porin 31HL shows approx. 29% or 24% identity to the primary structure of mitochondrial porins of Neurospora crassa and Saccharomyces cerevisiae. Partial data on mitochondrial porins from rat kidney and beef heart show sequence identity of about 90% to the human B cell porin elaborated here.     

Isolation and characterization of the Omp-PA porin from Porphyromonas asaccharolytica, determination of the omp-PA gene sequence and prediction of Omp-PA protein structure

A single monomeric porin, Omp-PA (37kDa), was isolated from the outer membrane of the gram-negative anaerobic rod Porphyromonas asaccharolytica. Further characterization revealed that this porin consists of two different fractions: a heat-modifiable fraction which in its denatured form migrated on SDS-PAGE as a protein with a molecular weight of 41kDa and a heat-resistant fraction which did not change its migration on SDS-PAGE after boiling. A liposome swelling assay revealed that only the heat-resistant fraction was able to transport sugars after its incorporation into the liposomes, although it did not discriminate between differently sized sugars. We hypothesize that the heat-modifiable fraction corresponds to the "closed" conformer of Omp-PA, whereas the heat-resistant fraction corresponds to the "open" conformer of the protein. Cloning of the omp-PA gene revealed an open reading frame of 1161 bases, with a predicted protein sequence of 387 amino acids. The mature protein consists of 366 amino acids with a calculated MW of 41,102Da and an estimated pI of 7.24. The C-terminal domain of Omp-PA is homologous to the characteristic OmpA signature domain (71% similarity with the OmpA consensus domain). Sequence comparison with other anaerobes from the Bacteroides family demonstrated homology across the entire ORF. Digestion of the P. asaccharolytica outer membrane analysis of trypsin-digested Omp-PA yielded two proteins migrating with apparent molecular weights of 37 and 27kDa. These data fully supported our hypothesis that the C-terminal domain of the two-domain "closed" conformer of Omp-PA was digested by trypsin, whereas the single domain beta-barrel "open" conformer was inaccessible to trypsin.     

Structure and function of pore-forming proteins from bacteria of the genus Yersinia: I. Isolation and a comparison of physicochemical properties and functional activity of Yersinia porins

The molecular organization and functional activity of porins isolated from the outer membrane (OM) of the Yersinia enterocolitica and three phylogenetically close nonpathogenic Yersinia species (Y. intermedia, Y. kristensenii, and Y. frederiksenii) cultured at 6-8 degrees C were comparatively studied for the first time. The proteins were isolated in two molecular forms (trimeric and monomeric), and their spatial structures were characterized by the methods of optical spectroscopy, CD and intrinsic protein fluorescence. The studied porins were shown to belong to the beta-structural proteins (they have 59-96% total beta structures and 0-17% alpha helices). The spatial structures of the proteins were demonstrated to depend on the nature of the detergent used for solubilization. Unlike the enterobacterial pore-forming proteins, the porin trimers are less stable to sodium dodecyl sulfate (SDS). The spatial structures of the porins become more compact after the substitution of octyl beta-D-glucoside for SDS: the content of beta structures increases and the accessibility of Trp residues to solvent decreases. It was established with the use of the technique of bilayer lipid membranes that the functional properties of the porins are similar to those of the OmpF proteins of Gram-negative bacteria. Trimers are functionally active forms of the porins. Special features of the pore-forming activity of the Yersinia porins were revealed to depend on the microorganism species and the value of the membrane potential.