Isolation of the outer membrane and characterization of the major outer membrane protein from Spirochaeta aurantia

Combined Use of Antimicrobial Peptides with Antiseptics against Multidrug-Resistant Bacteria: Pros and Cons

Antimicrobial peptides (AMPs) are acknowledged as a promising template for designing new antimicrobials. At the same time, existing toxicity issues and limitations in their pharmacokinetics make topical application one of the less complicated routes to put AMPs-based therapeutics into actual medical practice. Antiseptics are one of the common components for topical treatment potent against antibiotic-resistant pathogens but often with toxicity limitations of their own. Thus, the interaction of AMPs and antiseptics is an interesting topic that is also less explored than combined action of AMPs and antibiotics. Herein, we analyzed antibacterial, antibiofilm, and cytotoxic activity of combinations of both membranolytic and non-membranolytic AMPs with a number of antiseptic agents. Fractional concentration indices were used as a measure of possible effective concentration reduction achievable due to combined application. Cases of both synergistic and antagonistic interaction with certain antiseptics and surfactants were identified, and trends in the occurrence of these types of interaction were discussed. The data may be of use for AMP-based drug development and suggest that the topic requires further attention for successfully integrating AMPs-based products in the context of complex treatment. AMP/antiseptic combinations show promise for creating topical formulations with improved activity, lowered toxicity, and, presumably, decreased chances of inducing bacterial resistance. However, careful assessment is required to avoid AMP neutralization by certain antiseptic classes in either complex drug design or AMP application alongside other therapeutics/care products.

The leptospiral outer membrane

The outer membrane (OM) is the front line of leptospiral interactions with their environment and the mammalian host. Unlike most invasive spirochetes, pathogenic leptospires must be able to survive in both free-living and host-adapted states. As organisms move from one set of environmental conditions to another, the OM must cope with a series of conflicting challenges. For example, the OM must be porous enough to allow nutrient uptake, yet robust enough to defend the cell against noxious substances. In the host, the OM presents a surface decorated with adhesins and receptors for attaching to, and acquiring, desirable host molecules such as the complement regulator, Factor H.Factor H. On the other hand, the OM must enable leptospires to evade detection by the host's immune system on their way from sites of invasion through the bloodstream to the protected niche of the proximal tubule. The picture that is emerging of the leptospiral OM is that, while it shares many of the characteristics of the OMs of spirochetes and Gram-negative bacteria, it is also unique and different in ways that make it of general interest to microbiologists. For example, unlike most other pathogenic spirochetes, the leptospiral OM is rich in lipopolysaccharide (LPS). Leptospiral LPS is similar to that of Gram-negative bacteria but has a number of unique structural features that may explain why it is not recognized by the LPS-specific Toll-like receptor 4 of humans. As in other spirochetes, lipoproteins are major components of the leptospiral OM, though their roles are poorly understood. The functions of transmembrane outer membrane proteins (OMPs) in many cases are better understood, thanks to homologies with their Gram-negative counterparts and the emergence of improved genetic techniques. This chapter will review recent discoveries involving the leptospiral OM and its role in leptospiral physiology and pathogenesis.

Use of nonelectrolytes reveals the channel size and oligomeric constitution of the Borrelia burgdorferi P66 porin

In the Lyme disease spirochete Borrelia burgdorferi, the outer membrane protein P66 is capable of pore formation with an atypical high single-channel conductance of 11 nS in 1 M KCl, which suggested that it could have a larger diameter than 'normal' Gram-negative bacterial porins. We studied the diameter of the P66 channel by analyzing its single-channel conductance in black lipid bilayers in the presence of different nonelectrolytes with known hydrodynamic radii. We calculated the filling of the channel with these nonelectrolytes and the results suggested that nonelectrolytes (NEs) with hydrodynamic radii of 0.34 nm or smaller pass through the pore, whereas neutral molecules with greater radii only partially filled the channel or were not able to enter it at all. The diameter of the entrance of the P66 channel was determined to be ≤1.9 nm and the channel has a central constriction of about 0.8 nm. The size of the channel appeared to be symmetrical as judged from one-sidedness of addition of NEs. Furthermore, the P66-induced membrane conductance could be blocked by 80-90% by the addition of the nonelectrolytes PEG 400, PEG 600 and maltohexaose to the aqueous phase in the low millimolar range. The analysis of the power density spectra of ion current through P66 after blockage with these NEs revealed no chemical reaction responsible for channel block. Interestingly, the blockage of the single-channel conductance of P66 by these NEs occurred in about eight subconductance states, indicating that the P66 channel could be an oligomer of about eight individual channels. The organization of P66 as a possible octamer was confirmed by Blue Native PAGE and immunoblot analysis, which both demonstrated that P66 forms a complex with a mass of approximately 460 kDa. Two dimension SDS PAGE revealed that P66 is the only polypeptide in the complex.

Overproduction and purification of the luxR gene product: Transcriptional activator of the Vibrio fischeri luminescence system

Expression of Vibrio fischeri luminescence genes requires an inducer, termed autoinducer, and a positive regulatory element, the luxR gene product. A plasmid containing luxR under control of a tac promoter was engineered to overproduce this gene product. The overproduced luxR gene product was active in vivo, and its apparent monomeric molecular weight was indistinguishable from that of the protein encoded by luxR under control of its own promoter (M(r) 27,000). The new tac-luxR construct directed the synthesis of large quantities of the luxR gene product in induced Escherichia coli cells lacking other lux genes. In the presence of the other lux genes, overexpression of the tac-luxR construct was not detected. The overproduced luxR gene product, which formed cytoplasmic inclusion bodies, was purified and used in subsequent studies. Nonequilibrium pH gradient electrophoresis indicated that the protein was basic, and the amino-terminal 15 amino acids were sequenced. DNA-binding activity was detected by membrane filter binding assays; under the conditions used, the binding was not lux DNA-specific. Binding of tritium-labeled autoinducer to the luxR gene product was not detected, and autoinducer enhancement of the binding of the luxR gene product to DNA could not be detected reproducibly.

The structure and biological characteristics of the Spirochaeta aurantia outer membrane glycolipid LGLB

In an attempt to isolate lipopolysaccharide from Spirochaeta aurantia, Darveau-Hancock extraction of the cell mass was performed. While no lipopolysaccharide was found, two carbohydrate-containing compounds were detected. They were resolved by size-exclusion chromatography into high molecular mass (LGLA) and low molecular mass (LGLB) fractions. Here we present the results of the analysis of the glycolipid LGLB. Deacylation of LGLB with hydrazine and separation of the products by using anion-exchange chromatography gave two major products. Their structure was determined by using chemical methods, NMR and mass spectrometry. All monosaccharides had the D-configuration, and aspartic acid had the L-configuration. Intact LGLB contained two fatty groups at O-2 and O-3 of the glycerol residue. Nonhydroxylated C14 to C18 fatty acids were identified, which were predominantly unsaturated or branched. LGLB was able to gel Limulus amebocyte lysate, albeit at a lower level than that observed for Escherichia coli O113 lipopolysaccharide. However, even large amounts of LGLB were unable to stimulate any Toll-like receptor (TLR) examined, including TLR4 and TLR2, previously shown to be sensitive to lipopolysaccharide and glycolipids from diverse bacterial origins, including other spirochetes.

Nature of the genome of the saprophytic spirochete Spirochaeta aurantia and its ribosomal RNA operons

Using restriction endonucleases DraI, AseI, and I-CeuI in conjunction with pulsed-field gel electrophoresis, we have shown that Spirochaeta aurantia M1 possesses a circular 3.98-Mb genome. This is the second largest spirochete chromosome yet analyzed. The observation that the latter enzyme cuts in 3 places suggests the presence of 3 copies of the large subunit (23S) rRNA gene (rrl), which was confirmed by Southern hybridizations. The complete sequence of 2 of the ribosomal RNA operons was determined, revealing that their structure resembled that of the typical member of the bacterial superkingdom: rrs (16S; 1561 bp), tRNA, rrl (23S; 2972 bp), and rrf (5S; 110 bp). The S. aurantia rrs-rrl intergenic regions, as with Treponema denticola, contain genes specifying a 73-nt tRNA(Ala) (anticodon TGC) and a 77-nt tRNA(Ile) (anticodon GAT).

Acyl homoserine-lactone quorum-sensing signal generation

Acyl homoserine lactones (acyl-HSLs) are important intercellular signaling molecules used by many bacteria to monitor their population density in quorum-sensing control of gene expression. These signals are synthesized by members of the LuxI family of proteins. To understand the mechanism of acyl-HSL synthesis we have purified the Pseudomonas aeruginosa RhlI protein and analyzed the kinetics of acyl-HSL synthesis by this enzyme. Purified RhlI catalyzes the synthesis of acyl-HSLs from acyl-acyl carrier proteins and S-adenosylmethionine. An analysis of the patterns of product inhibition indicated that RhlI catalyzes signal synthesis by a sequential, ordered reaction mechanism in which S-adenosylmethionine binds to RhlI as the initial step in the enzymatic mechanism. Because pathogenic bacteria such as P. aeruginosa use acyl-HSL signals to regulate virulence genes, an understanding of the mechanism of signal synthesis and identification of inhibitors of signal synthesis has implications for development of quorum sensing-targeted antivirulence molecules.

Isolation and characterization of the outer membrane of Borrelia hermsii

The outer membrane of Borrelia hermsii has been shown by freeze-fracture analysis to contain a low density of membrane-spanning outer membrane proteins which have not yet been isolated or identified. In this study, we report the purification of outer membrane vesicles (OMV) from B. hermsii HS-1 and the subsequent identification of their constituent outer membrane proteins. The B. hermsii outer membranes were released by vigorous vortexing of whole organisms in low-pH, hypotonic citrate buffer and isolated by isopycnic sucrose gradient centrifugation. The isolated OMV exhibited porin activities ranging from 0.2 to 7.2 nS, consistent with their outer membrane origin. Purified OMV were shown to be relatively free of inner membrane contamination by the absence of measurable beta-NADH oxidase activity and the absence of protoplasmic cylinder-associated proteins observed by Coomassie blue staining. Approximately 60 protein spots (some of which are putative isoelectric isomers) with 25 distinct molecular weights were identified as constituents of the OMV enrichment. The majority of these proteins were also shown to be antigenic with sera from B. hermsii-infected mice. Seven of these antigenic proteins were labeled with [3H]palmitate, including the surface-exposed glycerophosphodiester phosphodiesterase, the variable major proteins 7 and 33, and proteins of 15, 17, 38, 42, and 67 kDa, indicating that they are lipoprotein constituents of the outer membrane. In addition, immunoblot analysis of the OMV probed with antiserum to the Borrelia garinii surface-exposed p66/Oms66 porin protein demonstrated the presence of a p66 (Oms66) outer membrane homolog. Treatment of intact B. hermsii with proteinase K resulted in the partial proteolysis of the Oms66/p66 homolog, indicating that it is surface exposed. This identification and characterization of the OMV proteins should aid in further studies of pathogenesis and immunity of tick-borne relapsing fever.

The Oms66 (p66) protein is a Borrelia burgdorferi porin

In this study we report the purification and characterization of a 66-kDa protein, designated Oms66, for outer membrane-spanning 66-kDa protein, that functions as a porin in the outer membrane (OM) of Borrelia burgdorferi. Oms66 was purified by fast-performance liquid chromatography and exhibited an average single-channel conductance of 9.62 +/- 0.37 nS in 1 M KCl, as evidenced by 581 individual insertional events in planar lipid bilayers. Electrophysiological characterization indicated that Oms66 was virtually nonselective between cations and anions and exhibited voltage-dependent closure with multiple substates. The amino acid sequence of tryptic peptides derived from purified Oms66 was identical to the deduced amino acid sequence of p66, a previously described surface-exposed protein of B. burgdorferi. Purified Oms66 was recognized by antiserum specific for p66 and serum from rabbits immune to challenge with virulent B. burgdorferi, indicating that p66 and Oms66 were identical proteins and that Oms66/p66 is an immunogenic protein in infected rabbits. In a methodology that reduces liposomal trapping and nonspecific interactions, native Oms66 was incorporated into liposomes, confirming that Oms66 is an outer membrane-spanning protein. Proteoliposomes containing Oms66 exhibited porin activity nearly identical to that of native, purified Oms66, indicating that reconstituted Oms66 retained native conformation. The use of proteoliposomes reconstituted with Oms66 and other Oms proteins provides an experimental system for determinating the relationship between conformation, protection, and biological function of these molecules.

Mutational analysis of the Vibrio fischeri LuxI polypeptide: critical regions of an autoinducer synthase

Synthesis of the Vibrio fischeri autoinducer, a signal involved in the cell density-dependent activation of bioluminescence, is directed by the luxI gene product. The LuxI protein catalyzes the synthesis of N-acyl-homoserine lactones from S-adenosylmethionine and acylated-acyl carrier protein. We have gained an appreciation of the LuxI regions and amino acid residues involved in autoinducer synthesis by isolating and analyzing mutations generated by random and site-specific mutagenesis of luxI. By random mutagenesis we isolated 13 different single amino acid substitutions in the LuxI polypeptide. Eleven of these substitutions resulted in no detectable autoinducer synthase activity, while the remaining two amino acid substitutions resulted in reduced but detectable activity. The substitutions that resulted in no detectable autoinducer synthase activity mapped to two small regions of LuxI. In Escherichia coli, wild-type luxI showed dominance over all of the mutations. Because autoinducer synthesis has been proposed to involve formation of a covalent bond between an acyl group and an active-site cysteine, we constructed site-directed mutations that altered each of the three cysteine residues in LuxI. All of the cysteine mutants retained substantial activity as an autoinducer synthase in E. coli. Based on the analysis of random mutations we propose a model in which there are two critical regions of LuxI, at least one of which is an intimate part of an active site, and based on the analysis of site-directed mutations we conclude that an active-site cysteine is not essential for autoinducer synthase activity.

Characterization of the Treponema denticola prtP gene encoding a prolyl-phenylalanine-specific protease (dentilisin)

A chymotrypsin-like protease from Treponema denticola ATCC 35405 was purified by chromatographic techniques. The purified enzyme consisted of three polypeptides (38, 43, and 72 kDa). The protease exhibited specificity for peptide bonds containing phenylalanine and proline at the P1 and P2 positions, respectively, and was classified as a serine protease on the basis of inhibition studies. Naturally occurring protease inhibitors such as alpha1-antitrypsin and alpha1-antichymotrypsin had no effect on enzymatic activity. The enzyme degraded fibronectin, alpha1-antitrypsin, and gelatin while weakly degrading the immunoglobulin G heavy chain and type IV collagen. N-terminal amino acid sequences were determined for the 43- and 72-kDa proteins. On the basis of these sequences, the genes coding for the 43- and 72-kDa proteins were isolated and sequenced. The open reading frame which codes for the 72-kDa protein was designated prtP. This gene consists of 2,169 bp and codes for a protein with an Mr of 77,471. The protein appeared to be composed of a signal peptide region followed by a prosequence and the mature protein domain. The deduced amino acid sequence exhibited similarity with that of the Bacillus subtilis serine protease subtilisin. The deduced properties of the sequence suggest that the 72-kDa protein is a chymotrypsin-like protease. However, the nature and function of the 43-kDa protein have not yet been determined.

Porin activity of the native and recombinant outer membrane protein Oms28 of Borrelia burgdorferi

The outer membrane-spanning (Oms) proteins of Borrelia burgdorferi have been visualized by freeze-fracture analysis but, until recently, not further characterized. We developed a method for the isolation of B. burgdorferi outer membrane vesicles and described porin activities with single-channel conductances of 0.6 and 12.6 nS in 1 M KCI. By using both nondenaturing isoelectric focusing gel electrophoresis and fast-performance liquid chromatography separation after detergent solubilization, we found that the 0.6-nS porin activity resided in a 28-kDa protein, designated Oms28. The oms28 gene was cloned, and its nucleotide sequence was determined. The deduced amino acid sequence of Oms28 predicted a 257-amino-acid precursor protein with a putative 24-amino-acid leader peptidase I signal sequence. Processed Oms28 yielded a mature protein with a predicted molecular mass of 25,363 Da. When overproduced in Escherichia coli, the Oms28 porin fractionated in part to the outer membrane. Sodium dodecyl sulfate-polyacrylamide gel-purified recombinant Oms28 from E. coli retained functional activity as demonstrated by an average single-channel conductance of 1.1 nS in the planar lipid bilayer assay. These findings confirmed that Oms28 is a B. burgdorferi porin, the first to be described. As such, it is potential relevance to the pathogenesis of Lyme borreliosis and to the physiology of the spirochete.

The rare outer membrane protein, OmpL1, of pathogenic Leptospira species is a heat-modifiable porin

The outer membranes of invasive spirochetes contain unusually small amounts of transmembrane proteins. Pathogenic Leptospira species produce a rare 31-kDa surface protein, OmpL1, which has a deduced amino acid sequence predictive of multiple transmembrane beta-strands. Studies were conducted to characterize the structure and function of this protein. Alkali, high-salt, and urea fractionation of leptospiral membranes demonstrated that OmpL1 is an integral membrane protein. The electrophoretic mobility of monomeric OmpL1 was modifiable by heat and reduction; complete denaturation of OmpL1 required prolonged boiling in sodium dodecyl sulfate (SDS), 8 M urea, and 2-mercaptoethanol. When solubilized in SDS at low temperature, a small proportion of OmpL1 exhibited an apparent molecular mass of approximately 90 kDa, indicating the existence of an SDS-unstable oligomer. OmpL1 dimers and trimers were demonstrated by nearest neighbor chemical cross-linking. In order to generate purified protein for functional studies, the ompL1 gene was ligated into the pMMB66 expression plasmid under control of the tac promoter. Although expression in Escherichia coli was toxic, most of the OmpL1 produced was found in the outer membrane, as determined by subcellular fractionation. Purified recombinant OmpL1 was reconstituted into planar lipid bilayers, demonstrating an average single channel conductance of 1.1 nS, similar to the major porin activity of native leptospiral membranes. These findings indicate that OmpL1 spans the leptospiral outer membrane and functions as a porin.

Synergistic binding of the Vibrio fischeri LuxR transcriptional activator domain and RNA polymerase to the lux promoter region

LuxR, the Vibrio fischeri luminescence gene (lux) activator, is the best-studied member of a family of bacterial transcription factors required for cell density-dependent expression of specific genes involved in associations with eukaryotic hosts. Neither LuxR nor any other LuxR homolog has been shown to bind DNA directly. We have purified the LuxR C-terminal transcriptional activator domain from extracts of recombinant Escherichia coli in which this polypeptide was expressed. The purified polypeptide by itself binds to lux regulatory DNA upstream of the lux box, a 20-bp palindrome that is required for LuxR activity in vivo, but it does not bind to the lux box. However, the LuxR C-terminal domain together with RNA polymerase protects a region including the lux box and the lux operon promoter from DNase I cleavage. There is very little protection of the lux operon promoter region from DNase I digestion in the presence of RNA polymerase alone. Apparently, there is a synergistic binding of the LuxR C-terminal domain and RNA polymerase to the promoter region. The upstream binding region for the purified polypeptide encompasses a binding site for cAMP receptor protein (CRP). Under some conditions, CRP binding can block the binding of the LuxR C-terminal domain to the upstream binding region, and it can also block the synergistic binding of the LuxR C-terminal domain and RNA polymerase to the lux box and luminescence gene promoter region. This description of DNA binding by the LuxR C-terminal domain should lead to an understanding of the molecular interactions of the LuxR family of transcriptional activators with regulatory DNA.

Isolation of the outer membranes from Treponema pallidum and Treponema vincentii

The outer membranes from Treponema pallidum subsp. pallidum and Treponema vincentii were isolated by a novel method. Purified outer membranes from T. pallidum and T. vincentii following sucrose gradient centrifugation banded at 7 and 31% (wt/wt) sucrose, respectively. Freeze fracture electron microscopy of purified membrane vesicles from T. pallidum and T. vincentii revealed an extremely low density of protein particles; the particle density of T. pallidum was approximately six times less than that of T. vincentii. The great majority of T. vincentii lipopolysaccharide was found in the outer membrane preparation. The T. vincentii outer membrane also contained proteins of 55 and 65 kDa. 125I-penicillin V labeling demonstrated that t. pallidum penicillin-binding proteins were found exclusively with the protoplasmic cylinders and were not detectable with purified outer membrane material, indicating the absence of inner membrane contamination. Isolated T. pallidum outer membrane was devoid of the 19-kDa 4D protein and the normally abundant 47-kDa lipoprotein known to be associated with the cytoplasmic membrane; only trace amounts of the periplasmic endoflagella were detected. Proteins associated with the T. pallidum outer membrane were identified by one- and two-dimensional electrophoretic analysis using gold staining and immunoblotting. Small amounts of strongly antigenic 17- and 45-kDa proteins were detected and shown to correspond to previously identified lipoproteins which are found principally with the cytoplasmic membrane. Less antigenic proteins of 65, 31 (acidic pI), 31 (basic pI), and 28 kDa were identified. Compared with whole-organism preparations, the 65- and the more basic 31-kDa proteins were found to be highly enriched in the outer membrane preparation, indicating that they may represent the T. pallidum rare outer membrane proteins. Reconstitution of solubilized T. pallidum outer membrane into lipid bilayer membranes revealed porin activity with two estimated channel diameters of 0.35 and 0.68 nm based on the measured single-channel conductances in 1 M KCl of 0.40 and 0.76 nS, respectively.

Outer membrane proteins of three pathogenic Leptospira species

The outer membrane proteins of seven reference strains of pathogenic Leptospira (L. alstoni serovar grippotyphosa, L. borgpetersenii serovar hardjo, and L. interrogans serovars autumnalis, bratislava, canicola, icterohaemorrhagiae, and pomona) were investigated to identify common surface-exposed outer membrane proteins. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of sodium-N-lauroylsarcosinate-insoluble outer membrane enriched fractions of the reference serovars and two field isolates of serovars hardjo and pomona revealed six common protein bands with approximate molecular masses of 77, 66, 42, 35.5, 24, and 18 kDa. At times the 35.5 kDa endoflagellar band resolved into two distinct bands, 35.5 kDa and 34 kDa. Immunoblotting of the same fractions using rabbit leptospiral antibodies showed six bands to be common (66, 59.5, 44, 42, 35.5, and 18 kDa). The 44 kDa band stained poorly with Coomassie blue but prominently by immunoblotting. Four reference strains (serovars bratislava, canicola, icterohaemorrhagiae, pomona), and two field isolates of serovar pomona and one of serovar bratislava were grown in low iron media to which the iron chelators 2,2'-dipyridyl or ethylenediaminehydroxyphenylacetic acid were added. No iron-dependent expression of outer membrane proteins was observed. The only difference observed between the outer membrane proteins when reference serovars of canicola or pomona were grown in dialysis bags in the peritoneum of swine or in vitro was the loss of the 77 kDa band from in vivo grown organisms. Treatment of whole leptospires with proteinase K did not remove the 77, 66, 59.5, or 42 kDa protein; these proteins may not be surface expressed or are inaccessible to the proteinase K. The 44 kDa band could not be evaluated by this method and the 18 kDa band was proteinase K resistant.

Molecular cloning and sequence analysis of the gene encoding OmpL1, a transmembrane outer membrane protein of pathogenic Leptospira spp

Pathogenic Leptospira spp. are spirochetes that have a low transmembrane outer membrane protein content relative to that of enteric gram-negative bacteria. In a previous study we identified a 31-kDa surface protein that was present in strains of Leptospira alstoni in amounts which correlated with the outer membrane particle density observed by freeze fracture electron microscopy (D. A. Haake, E. M. Walker, D. R. Blanco, C. A. Bolin, J. N. Miller, and M. A. Lovett, Infect. Immun. 59:1131-1140, 1991). The N-terminal amino acid sequence was used to design a pair of oligonucleotides which were utilized to screen a lambda ZAP II library containing EcoRI fragments of L. alstoni DNA. A 2.5-kb DNA fragment which contained the entire structural ompL1 gene was identified. The structural gene deduced from the sequence of this DNA fragment would encode a 320-amino-acid polypeptide with a 24-amino-acid leader peptide and a leader peptidase I cleavage site. Processing of OmpL1 results in a mature protein with a predicted molecular mass of 31,113 Da. Secondary-structure prediction identified repeated stretches of amphipathic beta-sheets typical of outer membrane protein membrane-spanning sequences. A topological model of OmpL1 containing 10 transmembrane segments is suggested. A recombinant OmpL1 fusion protein was expressed in Escherichia coli in order to immunize rabbits with the purified protein. Upon Triton X-114 extraction of L. alstoni and phase separation, anti-OmpL1 antiserum recognized a single band on immunoblots of the hydrophobic detergent fraction which was not present in the hydrophilic aqueous fraction. Immunoelectron microscopy with anti-OmpL1 antiserum demonstrates binding to the surface of intact L. alstoni. DNA hybridization studies indicate that the ompL1 gene is present in a single copy in all pathogenic Leptospira species that have been tested and is absent in nonpathogenic Leptospira species. OmpL1 may be the first spirochetal transmembrane outer membrane protein for which the structural gene has been cloned and sequenced.

Pore-forming properties of the major 53-kilodalton surface antigen from the outer sheath of Treponema denticola

A 53-kDa protein from the outer sheath of the oral spirochete Treponema denticola was purified to homogeneity and shown to reconstitute channels in black lipid bilayer model membranes. The channel had a single-channel conductance of 1.8 nS in 0.1 M KCl, making this the largest porin channel observed to date (estimated diameter, 3.4 nm). Electron micrographs of 53-kDa-protein-containing outer sheaths of T. denticola showed a regular hexagonal array of darker staining pits.

Genetic dissection of DNA binding and luminescence gene activation by the Vibrio fischeri LuxR protein

The Vibrio fischeri luminescence (lux) genes are regulated by the 250-amino-acid-residue LuxR protein and a V. fischeri metabolite termed autoinducer. The V. fischeri lux regulon consists of two divergently transcribed units. Autoinducer and LuxR activate transcription of the luxICDABE operon and autoregulate the luxR transcriptional unit. LuxR proteins with C-terminal truncations of up to 40 amino acid residues coded by plasmids with luxR 3'-deletion mutations are functional in negative autoregulation as demonstrated by using a luxR::lacZ transcriptional fusion as a luxR promoter probe in Escherichia coli. The truncated LuxR proteins showed little or no ability to activate transcription of luxICDABE, as indicated by using luminescence as a sensitive indicator of promoter strength in E. coli. Besides having no detectable activity as positive regulators of luxICDABE, LuxR proteins with C-terminal truncations of more than 40 amino acid residues had reduced or no detectable activity as negative autoregulators. The results suggest that amino acid residues in LuxR prior to no. 211 are sufficient for lux DNA binding. Residues in the region of 211 to 250 constitute a C-terminal tail that appears to be involved in activation of luxICDABE transcription either by interacting physically with the transcription initiation complex or by affecting lux DNA in the vicinity of the promoter.

The C-terminal region of the Vibrio fischeri LuxR protein contains an inducer-independent lux gene activating domain

The Vibrio fischeri luminescence genes are activated by an autoinducer and the 250-amino acid residue LuxR protein. To develop a general view of LuxR structure and function, a set of luxR 5'-deletion mutations was generated. Ten luxR mutant plasmids encoding active LuxR proteins with deletions ranging from residues 2-5 (delta 2-5) to residues 2-182 (delta 2-182) were studied. The degree of transcriptional activation of luminescence genes by the truncated LuxR proteins ranged from 0.01% to greater than 200% of the wild-type level. LuxR proteins with small deletions (up to delta 2-20) were active and remained autoinducer-dependent, LuxR proteins with deletions between residues 2-58 and 2-138 showed low activity and were not affected by autoinducer, and LuxR proteins with large deletions such as the delta 2-162 protein were highly active and autoinducer-independent. However, proteins with deletions equal to or greater than delta 2-20 were unable to autoregulate luxR. Our data indicate there is a C-terminal LuxR domain capable of functioning as a transcriptional activator. We suggest that an N-terminal region of LuxR starting between residues 20 and 58 and extending to the region of residues 138-162 masks the activator function of the C-terminal domain. Residues prior to position 20 are needed for autoregulatory function. Experiments showing that wild-type luxR is dominant over luxR genes coding the delta 2-58 through delta 2-138 proteins indicate the N-terminal arm masks lux DNA binding.

Chemical and biological activities of a 64-kilodalton outer sheath protein from Treponema denticola strains

This study examined the distribution of the major outer sheath proteins (MOSP) in several Treponema denticola strains and reports the isolation of a 64-kDa protein from the outer sheath of human clinical isolate T. denticola GM-1. The outer sheath was isolated by freeze-thaw procedures, and the distribution of outer sheath proteins was examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). T. denticola GM-1, MS25, SR-5, and three low-passage clinical isolates possessed an MOSP with a relative molecular mass of 60 to 64 kDa. This MOSP was absent in T. denticola ATCC 35404 (TD-4) and clinical isolate SR-4. The latter possessed an MOSP of 58 kDa. 125I labeling revealed both MOSP to be dissociated forms of higher-molecular-mass oligomeric units between 116 and 162 kDa. Two-dimensional SDS-PAGE confirmed the modifiability of these MOSP. Isoelectric focusing of the 64-kDa MOSP indicated a pI of 6.7. Immunoblots with antiserum to GM-1 whole cells revealed the 64-kDa protein to be immunogenic and not cross-reactive with the MOSP of TD-4 or SR-4, and monospecific antibody to the 64-kDa protein recognized common epitopes on the high-molecular-weight oligomeric protein. These antibodies did not react with any component of TD-4 whole cells in immunoblots or in immunogold electron microscopy. Fab fragments inhibited the adherence of T. denticola GM-1 to human gingival fibroblasts by 78% (1:1,600; 0.72 micrograms of protein per ml), while TD-4 adherence was not inhibited. Amino acid analysis revealed a slightly acidic protein, devoid of cysteine, with 36% hydrophobic residues. Cyanogen bromide fragmentation of the 64-kDa protein revealed that a 42-kDa fragment contained a T-L-D-L-A-L-D segment which was 100% homologous with an integrin alpha subunit of a human leukocyte adhesion glycoprotein p 150,95.

Factors in virulence expression and their role in periodontal disease pathogenesis

The classic progression of the development of periodontitis with its associated formation of an inflammatory lesion is characterized by a highly reproducible microbiological progression of a Gram-positive microbiota to a highly pathogenic Gram-negative one. While this Gram-negative microbiota is estimated to consist of at least 300 different microbial species, it appears to consist of a very limited number of microbial species that are involved in the destruction of periodontal diseases. Among these "putative periodontopathic species" are members of the genera Porphyromonas, Bacteroides, Fusobacterium, Wolinella, Actinobacillus, Capnocytophaga, and Eikenella. While members of the genera Actinomyces and Streptococcus may not be directly involved in the microbial progression, these species do appear to be essential to the construction of the network of microbial species that comprise both the subgingival plaque matrix. The temporal fluctuation (emergence/disappearance) of members of this microbiota from the developing lesion appears to depend upon the physical interaction of the periodontal pocket inhabitants, as well as the utilization of the metabolic end-products of the respective species intimately involved in the disease progression. A concerted action of the end-products of prokaryotic metabolism and the destruction of host tissues through the action of a large number of excreted proteolytic enzymes from several of these periodontopathogens contribute directly to the periodontal disease process.(ABSTRACT TRUNCATED AT 250 WORDS)

N-terminal amino acid sequences and amino acid compositions of the Spirochaeta aurantia flagellar filament polypeptides

The amino-terminal sequences and amino acid compositions of the three major and two minor polypeptides constituting the filaments of Spirochaeta aurantia periplasmic flagella were determined. The amino-terminal sequence of the major 37.5-kDa outer layer polypeptide is identical to the sequence downstream of the proposed signal peptide of the protein encoded by the S. aurantia flaA gene. However, the amino acid composition of the 37.5-kDa polypeptide is not in agreement with that inferred from the sequence of flaA. The 34- and 31.5-kDa major filament core polypeptides and the 33- and 32-kDa minor core polypeptides show a striking similarity to each other, and the amino-terminal sequences of these core polypeptides show extensive identity with homologous proteins from members of other genera of spirochetes. An additional 36-kDa minor polypeptide that occurs occasionally in preparations of S. aurantia periplasmic flagella appears to be mixed with the 37.5-kDa outer layer polypeptide or a degradation product of this polypeptide.

Critical regions of the Vibrio fischeri luxR protein defined by mutational analysis

Expression of Vibrio fischeri luminescence genes requires an inducer, termed autoinducer, and a positive regulatory element, the luxR gene product. A plasmid containing a tac promoter-controlled luxR was mutagenized in vitro with hydroxylamine, and luxR mutant plasmids were identified by their inability to complement a luxR deletion mutation in trans. Sixteen luxR mutant plasmids were obtained, ten of which encoded full-length but inactive luxR gene products as demonstrated by a Western immunoblot analysis. The effects of 1 of the 10 mutations could be overcome by the addition of autoinducer at a high concentration. The mutations in each of the 10 mutant plasmids that directed the synthesis of an inactive LuxR protein were identified by DNA sequencing. Of the 10 proteins encoded by the mutant luxR plasmids, 9 differed from the normally active LuxR in only a single amino acid residue. The amino acid residue substitutions in the proteins encoded by the nine mutant luxR genes clustered in two regions. One region around the middle of the polypeptide encoded by luxR was hypothesized to represent an autoinducer-binding domain, and the other region towards the carboxy terminus of the gene product was hypothesized to constitute a lux operator DNA-binding domain or a lux operator DNA recognition domain.

Biochemical and cytological analysis of the complex periplasmic flagella from Spirochaeta aurantia

The periplasmic flagella of Spirochaeta aurantia were isolated and were found to be ultrastructurally and biochemically complex. Generally, flagellar filaments were 18 to 20 nm in diameter and appeared to consist of an 11 to 13-nm-wide inner region and an outer layer. The hook-basal body region consisted of two closely apposed disks connected to a hook by a rod. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified flagella together with a Western blot analysis of a motility mutant that produces hooks and basal bodies but not flagellar filaments revealed that the filaments were composed of three major polypeptides of 37,500, 34,000, and 31,500 apparent molecular weight (37.5K, 34K, and 31.5K polypeptides) and three minor polypeptides of 36,000, 33,000, and 32,000 apparent molecular weight (36K, 33K, and 32K polypeptides). Purified hook-basal body preparations were greatly enriched in three polypeptides in the range of 62,000 to 66,000 apparent molecular weight. Immunogold labeling experiments with a monoclonal antibody specific for the 37.5K flagellin and one that reacts with an epitope common to the 36K, 34K, 33K, 32K, and 31.5K flagellins revealed that the 37.5K major polypeptide was a component of the outer layer, whereas one or more of the other polypeptides constituted the core.