Differences in synovial fluid levels of matrix metalloproteinases suggest separate mechanisms of pathogenesis in Lyme arthritis before and after antibiotic treatment

The cause of persistent arthritis in patients with Lyme disease who have received standard antibiotic therapy remains an area of debate. In this study, synovial fluid levels of matrix metalloproteinases (MMPs) were compared in persons with untreated and antibiotic-resistant Lyme arthritis. Levels of MMP-1 and MMP-3, as determined by ELISA, were higher in untreated patients (P=.0064 and P=.002, respectively), whereas levels of MMP-8 and MMP-9 were higher in antibiotic-resistant patients (P=.0002 and P=.0014, respectively). In vitro studies of chondrocyte cultures infected with Borrelia burgdorferi revealed induction of MMP-1 and MMP-3 but not of MMP-8 or MMP-9. Neither Staphylococcus aureus nor lipopolysaccharide stimulated MMP-1 or MMP-3 release from these cells. The mechanism of recognition of B. burgdorferi may be through CD14 and toll-like receptor-2, which were up-regulated in the presence of B. burgdorferi. These findings suggest different stimuli for MMP induction in untreated and antibiotic-resistant Lyme arthritis.

Genomics-based identification of targets in pathogenic bacteria for potential therapeutic and diagnostic use

The availability of numerous complete microbial genome sequences has profoundly altered our understanding of a number of fundamental biological processes. For example the enzymes involved in aminoacyl-tRNA (AA-tRNA) synthesis, the key process responsible for the accuracy of protein synthesis, have been found to be highly species-specific. In particular, a number of pathogens contain certain pathways of AA-tRNA synthesis that are unrelated to those found in their mammalian hosts. Since AA-tRNA synthesis is indispensable for cell viability, the discovery of pathogen-specific pathways and enzymes presents novel therapeutic and diagnostic targets. Here we will review recent advances in the elucidation of AA-tRNA synthesis pathways and discuss the possible pharmaceutical exploitation of these discoveries. In particular, the integration of genomic and biochemical approaches to identify novel targets for the treatment of Chlamydial infections and the diagnosis and treatment of Lyme disease will be presented.

Functional testing of putative oligopeptide permease (Opp) proteins of Borrelia burgdorferi: a complementation model in opp(-) Escherichia coli

Studies of the protein function of Borrelia burgdorferi have been limited by a lack of tools for manipulating borrelial DNA. We devised a system to study the function of a B. burgdorferi oligopeptide permease (Opp) orthologue by complementation with Escherichia coli Opp proteins. The Opp system of E. coli has been extensively studied and has well defined substrate specificities. The system is of interest in B. burgdorferi because analysis of its genome has revealed little identifiable machinery for synthesis or transport of amino acids and only a single intact peptide transporter operon. As such, peptide uptake may play a major role in nutrition for the organism. Substrate specificity for ABC peptide transporters in other organisms is determined by their substrate binding protein. The B. burgdorferi Opp operon differs from the E. coli Opp operon in that it has three separate substrate binding proteins, OppA-1, -2 and -3. In addition, B. burgdorferi has two OppA orthologues, OppA-4 and -5, encoded on separate plasmids. The substrate binding proteins interact with integral membrane proteins, OppB and OppC, to transport peptides into the cell. The process is driven by two ATP binding proteins, OppD and OppF. Using opp-deleted E. coli mutants, we transformed cells with B. burgdorferi oppA-1, -2, -4 or -5 and E. coli oppBCDF. All of the B. burgdorferi OppA proteins are able to complement E. coli OppBCDF to form a functional Opp transport system capable of transporting peptides for nutritional use. Although there is overlap in substrate specificities, the substrate specificities for B. burgdorferi OppAs are not identical to that of E. coli OppA. Transport of toxic peptides by B. burgdorferi grown in nutrient-rich medium parallels borrelial OppA substrate specificity in the complementation system. Use of this complementation system will pave the way for more detailed studies of B. burgdorferi peptide transport than currently available tools for manipulating borrelial DNA will allow.

Enzyme activities of Borrelia burgdorferi sensu lato

Activities of 19 enzymes were tested by the API ZYM system in 13 strains of Borrelia burgdorferi sensu lato (B. burgdorferi sensu stricto, B. afzelii, B. garinii, B. lusitaniae, B. valaisiana) grown in liquid BSK-H medium supplemented with rabbit serum. All strains produced acid phosphatase, esterase (C4), esterase-lipase (C8), leucine arylamidase and naphthol-AS-BI-phosphohydrolase. Nine strains also produced alkaline phosphatase, and three strains produced alpha-glucosidase. The API ZYM system probably cannot be used for differentiation between B. burgdorferi sensu lato genomospecies.

Context-dependent anticodon recognition by class I lysyl-tRNA synthetases

Lysyl-tRNA synthesis is catalyzed by two unrelated families of aminoacyl-tRNA synthetases. In most bacteria and all eukarya, the known lysyl-tRNA synthetases (LysRSs) are subclass IIb-type aminoacyl-tRNA synthetases, whereas many archaea and a scattering of bacteria contain an unrelated class I-type LysRS. Examination of the recognition of partially modified tRNA(Lys) anticodon variants by a bacterial (from Borrelia burgdorferi) and an archaeal (from Methanococcus maripaludis) class I lysyl-tRNA synthetase revealed differences in the pattern of anticodon recognition between the two enzymes. U35 and U36 were both important for recognition by the B. burgdorferi enzyme, whereas only U36 played a role in recognition by M. maripaludis LysRS. Examination of the phylogenetic distribution of class I LysRSs suggested a correlation between recognition of U35 and U36 and the presence of asparaginyl-tRNA synthetase (AsnRS), which also recognizes U35 and U36 in the anticodon of tRNA(Asn). However, the class II LysRS of Helicobacter pylori, an organism that lacks AsnRS, also recognizes both U35 and U36, indicating that the presence of AsnRS has solely influenced the phylogenetic distribution of class I LysRSs. These data suggest that competition between unrelated aminoacyl-tRNA synthetases for overlapping anticodon sequences is a determinant of the phylogenetic distribution of extant synthetase families. Such patterns of competition also provide a basis for the two separate horizontal gene transfer events hypothesized in the evolution of the class I lysyl-tRNA synthetases.

Differentiation of Borrelia burgdorferi sensu lato on the basis of RNA polymerase gene (rpoB) sequences

We determined the nucleotide sequences (329 bp) of the rpoB DNAs from 22 reference strains of Borrelia. No insertions or deletions were observed. Deduced amino acid sequences of amplified rpoB DNA comprised 109 amino acid residues (N(450) to M(558) [Escherichia coli numbering]). All amino acid sequences were identical with the exception of those of Borrelia lusitaniae PotiB2 (T(461)-->A) and B. bissettii DN127 (I(498)-->V). Each species of B. burgdorferi sensu lato was differentiated as a distinct entity in the phylogenetic tree constructed by a neighbor-joining method. B. burgdorferi sensu lato could be distinguished from B. turicatae and B. hermsii, which are associated with relapsing fever. Seventeen Korean isolates could be identified by PCR-linked direct sequencing and restriction analysis of the rpoB DNA. These results suggest that rpoB DNA is useful for identification and characterization of Borrelia. In addition, we developed the rapid species identification method using the species-specific primer sets based on rpoB gene sequences.

Crystal structure at 2.4 A resolution of Borrelia burgdorferi inosine 5'-monophosphate dehydrogenase: evidence of a substrate-induced hinged-lid motion by loop 6

The conversion of inosine 5'-monophosphate (IMP) to xanthosine 5'-monophosphate (XMP) is the committed and rate-limiting reaction in de novo guanine nucleotide biosynthesis. Inosine 5'- monophosphate dehydrogenase (IMPDH) is the enzyme that catalyzes the oxidation of IMP to XMP with the concomitant reduction of nicotinamide adenine dinucleotide (from NAD(+) to NADH). Because of its critical role in purine biosynthesis, IMPDH is a drug design target for anticancer, antiinfective, and immunosuppressive chemotherapy. We have determined the crystal structure of IMPDH from Borrelia burgdorferi, the bacterial spirochete that causes Lyme disease, with a sulfate ion bound in the IMP phosphate binding site. This is the first structure of IMPDH in the absence of substrate or cofactor where the active-site loop (loop 6), which contains the essential catalytic residue Cys 229, is clearly defined in the electron density. We report that a seven residue region of loop 6, including Cys229, is tilted more than 6 A away from its position in substrate- or substrate analogue-bound structures of IMPDH, suggestive of a conformational change. The location of this loop between beta6 and alpha6 links IMPDH to a family of beta/alpha barrel enzymes known to utilize this loop as a functional lid during catalysis. Least-squares minimization, root-mean-square deviation analysis, and inspection of the molecular surface of the loop 6 region in the substrate-free B. burgdorferi IMPDH and XMP-bound Chinese hamster IMPDH show that loop 6 follows a similar pattern of hinged rigid-body motion and indicates that IMPDH may be using loop 6 to bind and sequester substrate and to recruit an essential catalytic residue.

Disruption of the Borrelia burgdorferi gac gene, encoding the naturally synthesized GyrA C-terminal domain

The C-terminal domain of the A subunit of DNA gyrase, which we term Gac, is naturally synthesized in Borrelia burgdorferi as an abundant DNA-binding protein. Full-length GyrA, which includes the C-terminal domain, is also synthesized by the spirochete and functions as a subunit of DNA gyrase. We have disrupted synthesis of Gac as an independent protein and demonstrated that it is not essential for growth in a coumarin-resistant background. We detected no alterations in DNA maintenance, condensation, or topology in B. burgdorferi lacking this small DNA-binding protein.

Transcriptional analysis of a superoxide dismutase gene of Borrelia burgdorferi

A single superoxide dismutase (Sod) gene was identified in Borrelia burgdorferi strains, Borrelia afzelii Ple and Borrelia garinii Pbi. Recombinant enzymatic activity was detected only when sod expression was controlled by the lacZ promoter in the cloning vector. Northern blot analysis with sod- or secA-specific probes identified a common 3.7-kb transcript. Reverse transcriptase-PCR analysis confirmed that secA and sod constitute a single transcriptional unit in B. burgdorferi. A transcriptional start site of this operon, containing -10 and -35 regions of a sigma(70)-type promoter, was mapped to 100 bp upstream of the ATG start codon of secA.

Borrelia burgdorferi induces matrix metalloproteinases by neural cultures

Matrix metalloproteinases (MMPs) are associated with chronic neurologic diseases such as multiple sclerosis and senile dementia. Lyme disease is a multisystemic infection involving the nervous system, skin, joints, and heart. Neurologic manifestations of chronic Lyme disease include encephalopathy and cranial and peripheral neuropathy. Borrelia burgdorferi, the spirochaete causing Lyme disease, has been cultured from the cerebrospinal fluid (CSF), and B. burgdorferi DNA is frequently detected in the CSF of patients with Lyme neuroborreliosis. We used cerebral and cerebellar primary cultures to determine whether B. burgdorferi induces the production of MMPs by primary neural cultures. B. burgdorferi in a dose- and time-dependent manner induced the expression of MMP-9 by primary neural cultures but had no effect on the expression of MMP-2. Human and rat type I astrocytes expressed MMP-9 when incubated with B. burgdorferi in the same manner as primary neural cultures. This response may play a role in the symptomatology and the pathogenesis of Lyme neuroborreliosis.

Expression, characterization, and crystallization of the pyrophosphate-dependent phosphofructo-1-kinase of Borrelia burgdorferi

The two genes for the putative pyrophosphate-dependent phosphofructokinases (PPi-PFKs) of Borrelia burgdorferi were cloned by PCR and expressed in Escherichia coli, and their protein products were purified to near homogeneity. The larger of the two gene products, a 62-kDa protein, is an active PPi-PFK and exists in solution as a dimer. It has apparent K(m) values for fructose 6-P and PPi of 109 and 15 microM, respectively, and a pH optimum of 6.4 to 7.2. The 62-kDa protein was crystallized and subjected to preliminary diffraction analysis. The smaller gene product, a 48-kDa protein, exists in solution as a higher polymer and shows no ATP- or PPi-dependent activity, despite having a secondary structure as estimated by circular dichroism that is not significantly different from that of other PFKs.

IMP dehydrogenase: mechanism of action and inhibition

Inosine monophosphate dehydrogenase (IMPDH) catalyzes the conversion of IMP to XMP with the concomitant reduction of NAD to NADH. This reaction is the rate-limiting step in guanine nucleotide biosynthesis. IMPDH is a proven target for immunosuppressive, anticancer and antiviral chemotherapy, and may also be a target for antimicrobial agents. IMPDH is activated by monovalent cations, and one monovalent cation binding site appears to have been identified. The mechanism of IMPDH involves formation and hydrolysis of a covalent enzyme intermediate (E-XMP*) in a reaction reminiscent of glyceraldehyde-3-phosphate dehydrogenase. Substrates bind to IMPDH in a random order, hydride transfer is fast and NADH release precedes hydrolysis of E-XMP*. The hydrolysis of E-XMP* is at least partially rate-limiting. Two inhibitors, mizoribine-monophosphate and a fat base nucleotide appear to act as transition state analogs. In contrast, MPA inhibits by sequestering E-XMP.

IMP dehydrogenase : structural aspects of inhibitor binding

Inosine monophosphate dehydrogenase (IMPDH, E.C. 1.1.1.205) is recognized as an important target for both antileukemic and immunosuppressive therapy. IMPDH catalyzes the NAD-dependent oxidation of inosine 5 monophosphate (IMP) to xanthosine 5 monophosphate. Several classes of IMPDH inhibitors are now in use or under development. These include agents that bind at either the substrate site (e.g. ribavirin and mizoribine) or at the NAD site (mycophenolic acid and thiazole-4-carboxamide adenine dinucleotide). All suffer from some degree of toxicity and/or susceptibility to metabolic inactivation. The finding that IMPDH exists as two isoforms, one of which (type II) is induced in tumor cells, has led to the search for potentially more effective isoform-specific agents. Recently, a number of crystal structures of IMPDH have become available. These include structures of the human type II, hamster, Tritrichomonas foetus, Streptococcus pyogenes and Borrelia burgdorferi enzymes. Each structure crystallizes as a tetramer of a/b barrels, with the active site located partly at the monomer-monomer interface. The substrate and cofactor bind in a continuous cleft on the C-terminal face of each barrel. The IMP base is well positioned to stack against the NAD nicotinamide ring to facilitate hydride transfer. The active site cleft is further bounded by a highly flexible flap and loop. These structures reveal enzyme-ligand interactions which suggest strategies for the design of improved inhibitors.

Differential signatures of bacterial and mammalian IMP dehydrogenase enzymes

IMP dehydrogenase (IMPDH) is an essential enzyme of de novo guanine nucleotide synthesis. IMPDH inhibitors have clinical utility as antiviral, anticancer or immunosuppressive agents. The essential nature of this enzyme suggests its therapeutic applications may be extended to the development of antimicrobial agents. Bacterial IMPDH enzymes show biochemical and kinetic characteristics that are different than the mammalian IMPDH enzymes, suggesting IMPDH may be an attractive target for the development of antimicrobial agents. We suggest that the biochemical and kinetic differences between bacterial and mammalian enzymes are a consequence of the variance of specific, identifiable amino acid residues. Identification of these residues or combination of residues that impart this mammalian or bacterial enzyme signature is a prerequisite for the rational identification of agents that specifically target the bacterial enzyme. We used sequence alignments of IMPDH proteins to identify sequence signatures associated with bacterial or eukaryotic IMPDH enzymes. These selections were further refined to discern those likely to have a role in catalysis using information derived from the bacterial and mammalian IMPDH crystal structures and site-specific mutagenesis. Candidate bacterial sequence signatures identified by this process include regions involved in subunit interactions, the active site flap and the NAD binding region. Analysis of sequence alignments in these regions indicates a pattern of catalytic residues conserved in all enzymes and a secondary pattern of amino acid conservation associated with the major phylogenetic groups. Elucidation of the basis for this mammalian/bacterial IMPDH signature will provide insight into the catalytic mechanism of this enzyme and the foundation for the development of highly specific inhibitors.

Esterases in serum-containing growth media counteract chloramphenicol acetyltransferase activity in vitro

The spirochete Borrelia burgdorferi was unexpectedly found to be as susceptible to diacetyl chloramphenicol, the product of the enzyme chloramphenicol acetyltransferase, as it was to chloramphenicol itself. The susceptibilities of Escherichia coli and Bacillus subtilis, as well as that of B. burgdorferi, to diacetyl chloramphenicol were then assayed in different media. All three species were susceptible to diacetyl chloramphenicol when growth media were supplemented with rabbit serum or, to a lesser extent, human serum. Susceptibility of E. coli and B. subtilis to diacetyl chloramphenicol was not observed in the absence of serum, when horse serum was used, or when the rabbit or human serum was heated first. In the presence of 10% rabbit serum, a strain of E. coli bearing the chloramphenicol acetyltransferase (cat) gene had a fourfold-lower resistance to chloramphenicol than in the absence of serum. A plate bioassay for chloramphenicol activity showed the conversion by rabbit, mouse, and human sera but not bacterial cell extracts or heated serum of diacetyl chloramphenicol to an inhibitory compound. Deacetylation of acetyl chloramphenicol by serum components was demonstrated by using fluorescent substrates and thin-layer chromatography. These studies indicate that esterases of serum can convert diacetyl chloramphenicol back to an active antibiotic, and thus, in vitro findings may not accurately reflect the level of chloramphenicol resistance by cat-bearing bacteria in vivo.

Substrate recognition by class I lysyl-tRNA synthetases: a molecular basis for gene displacement

Lysyl-tRNA synthetases (LysRSs) are unique amongst the aminoacyl-tRNA synthetases in being composed of unrelated class I and class II enzymes. To allow direct comparison between the two types of LysRS, substrate recognition by class I LysRSs was examined. Genes encoding both an archaeal and a bacterial class I enzyme were able to rescue an Escherichia coli strain deficient in LysRS, indicating their ability to functionally substitute for a class II LysRS in vivo. In vitro characterization showed lysine activation and recognition to be tRNA-dependent, an attribute of several class I, but not class II, aminoacyl-tRNA synthetases. Examination of tRNA recognition showed that class I LysRSs recognize the same elements in tRNALys as their class II counterparts, namely the discriminator base (N73) and the anticodon. This sequence-specific recognition of the same nucleotides in tRNALys by the two unrelated types of enzyme suggests that tRNALys predates at least one of the LysRSs in the evolution of the translational apparatus. The only observed variation in recognition was that the G2.U71 wobble pair of spirochete tRNALys acts as antideterminant for class II LysRS but does not alter class I enzyme recognition. This difference in tRNA recognition strongly favors the use of a class I-type enzyme to aminoacylate particular tRNALys species and provides a molecular basis for the observed displacement of class II by class I LysRSs in certain bacteria.

Isolation of Borrelia burgdorferi from ticks in the Highlands of Scotland

Borrelia burgdorferi, the causative agent of Lyme disease, was first isolated in 1982 and since then has been regularly isolated from ticks and clinical material in both Continental Europe and the USA. However, only three isolations have been reported in Britain. During the summer of 1997, 128 ticks were collected from two sites in the Highlands of Scotland and examined by the polymerase chain reaction (PCR) and culture. Eleven fresh isolates were obtained from culture and passed up to 22 times. Seven of the tick emulsions were also positive by flagellin gene PCR, and a further one was positive by PCR but negative on culture. All 11 isolate cultures were positive by the flagellin gene PCR. Further studies on four of these isolates confirmed their identity by immunofluorescence, but also detected possible differences between them and B. burgdorferi ACA-1 by enzyme profiles and by PCR with OspA gene primers. Culture of these new strains provides antigens that should improve diagnostic serological tests in Britain.

The serine, threonine, and/or tyrosine-specific protein kinases and protein phosphatases of prokaryotic organisms: a family portrait

Inspection of the genomes for the bacteria Bacillus subtilis 168, Borrelia burgdorferi B31, Escherichia coli K-12, Haemophilus influenzae KW20, Helicobacter pylori 26695, Mycoplasma genitalium G-37, and Synechocystis sp PCC 6803 and for the archaeons Archaeoglobus fulgidus VC-16 DSM4304, Methanobacterium thermoautotrophicum delta H, and Methanococcus jannaschii DSM2661 revealed that each contains at least one ORF whose predicted product displays sequence features characteristic of eukaryote-like protein-serine/threonine/tyrosine kinases and protein-serine/threonine/tyrosine phosphatases. Orthologs for all four major protein phosphatase families (PPP, PPM, conventional PTP, and low molecular weight PTP) were present in the bacteria surveyed, but not all strains contained all types. The three archaeons surveyed lacked recognizable homologs of the PPM family of eukaryotic protein-serine/threonine phosphatases; and only two prokaryotes were found to contain ORFs for potential phosphatases from all four major families. Intriguingly, our searches revealed a potential ancestral link between the catalytic subunits of microbial arsenate reductases and the protein-tyrosine phosphatases; they share similar ligands (arsenate versus phosphate) and features of their catalytic mechanism (formation of arseno-versus phospho-cysteinyl intermediates). It appears that all prokaryotic organisms, at one time, contained the genetic information necessary to construct protein phosphorylation-dephosphorylation networks that target serine, threonine, and/or tyrosine residues on proteins. However, the potential for functional redundancy among the four protein phosphatase families has led many prokaryotic organisms to discard one, two, or three of the four.

Homologues of helicase genes priA and ruvAB of Borrelia burgdorferi, the Lyme borreliosis agent

A DNA library of strain HB19 from Borrelia burgdorferi sensu stricto, an agent of Lyme borreliosis, was constructed in the cosmid pLA2917. Genes involved in initiation of DNA replication and resolution of recombination intermediates (Holliday junctions) were found on a 23-kbp region up to 0.7 kbp of the "left" extremity of the linear chromosome in representative species of B. burgdorferi sensu lato. The potential ruvB gene, located at 22 kbp from the left telomere, was identified by the similarity of its deduced amino acid sequence to RuvB (helicases) of other bacteria. B. burgdorferi ruvB is part of an operon which comprises the homologues of ruvA, queA and pfbB. Expression of the B. burgdorferi ruvB and ruvA genes renders a wild-type Escherichia coli sensitive to UV light and mitomycin, indicative of negative complementation. priA, which encodes the potential recognition factor for the primosome assembly site, was found at 15 kbp from the left telomere. RuvB and PriA sequences have motifs characteristic of helicases: a DExH box and an ATP binding site.

Oligopeptide permease in Borrelia burgdorferi: putative peptide-binding components encoded by both chromosomal and plasmid loci

To elucidate the importance of oligopeptide permease for Borrelia burgdorferi, the agent of Lyme disease, a chromosomal locus in B. burgdorferi that encodes homologues of all five subunits of oligopeptide permease has been identified and characterized. B. burgdorferi has multiple copies of the gene encoding the peptide-binding component, OppA; three reside at the chromosomal locus and two are on plasmids. Northern analyses indicate that each oppA gene is independently transcribed, although the three chromosomal oppA genes are also expressed as bi- and tri-cistronic messages. Induction of one of the plasmid-encoded oppA genes was observed following an increase in temperature, which appears to be an important cue for adaptive responses in vivo. The deduced amino acid sequences suggest that all five borrelial oppA homologues are lipoproteins, but the protease-resistance of at least one of them in intact bacteria is inconsistent with outer-surface localization. Insertional inactivation of a plasmid-encoded oppA gene demonstrates that it is not essential for growth in culture.

Archaeal-type lysyl-tRNA synthetase in the Lyme disease spirochete Borrelia burgdorferi

Lysyl-tRNAs are essential for protein biosynthesis by ribosomal mRNA translation in all organisms. They are synthesized by lysyl-tRNA synthetases (EC 6.1.1.6), a group of enzymes composed of two unrelated families. In bacteria and eukarya, all known lysyl-tRNA synthetases are subclass IIc-type aminoacyl-tRNA synthetases, whereas some archaea have been shown to contain an unrelated class I-type lysyl-tRNA synthetase. Examination of the preliminary genomic sequence of the bacterial pathogen Borrelia burgdorferi, the causative agent of Lyme disease, indicated the presence of an open reading frame with over 55% similarity at the amino acid level to archaeal class I-type lysyl-tRNA synthetases. In contrast, no coding region with significant similarity to any class II-type lysyl-tRNA synthetase could be detected. Heterologous expression of this open reading frame in Escherichia coli led to the production of a protein with canonical lysyl-tRNA synthetase activity in vitro. Analysis of B. burgdorferi mRNA showed that the lysyl-tRNA synthetase-encoding gene is highly expressed, confirming that B. burgdorferi contains a functional class I-type lysyl-tRNA synthetase. The detection of an archaeal-type lysyl-tRNA synthetase in B. burgdorferi and other pathogenic spirochetes, but not to date elsewhere in bacteria or eukarya, indicates that the gene that encodes this enzyme has a common origin with its orthologue from the archaeal kingdom. This difference between the lysyl-tRNA synthetases of spirochetes and their hosts may be readily exploitable for the development of anti-spirochete therapeutics.

Identification of superoxide dismutase activity in Borrelia burgdorferi

Infective and noninfective strains of Borrelia burgdorferi, along with Borrelia afzelii and Borrelia garinii, possessed a single iron-containing superoxide dismutase (SOD). None of the Lyme disease spirochetes tested possessed catalase or peroxidase activities. The borrelial SOD was not inducible by growth with increased oxygen concentrations and thus appeared to be produced constitutively.

Expression, purification, and characterization of inosine 5'-monophosphate dehydrogenase from Borrelia burgdorferi

Inosine 5'-monophosphate dehydrogenase (IMPDH) is the rate-limiting enzyme in de novo guanine nucleotide biosynthesis. IMPDH converts IMP to xanthosine 5'-monophosphate with concomitant conversion of NAD+ to NADH. All IMPDHs characterized to date contain a 130-residue "subdomain" that extends from an N-terminal loop of the alpha/beta barrel domain. The role of this subdomain is unknown. An IMPDH homolog has been cloned from Borrelia burgdorferi, the causative agent of Lyme disease (Margolis, N., Hogan, D., Tilly, K., and Rosa, P. A. (1994) J. Bacteriol. 176, 6427-6432). This homolog has replaced the subdomain with a 50-residue segment of unrelated sequence. We have expressed and characterized the B. burgdorferi IMPDH homolog. This protein has IMPDH activity, which unequivocally demonstrates that the subdomain is not required for catalytic activity. The monovalent cation and dinucleotide binding sites of B. burgdorferi IMPDH are significantly different from those of human IMPDH. Therefore, these sites are targets for the design of specific inhibitors for B. burgdorferi IMPDH. Such inhibitors might be new treatments for Lyme disease.

Cloning and expression of the Borrelia burgdorferi lon gene

The ATP-dependent protease Lon (La) of Escherichia coli degrades abnormal proteins and is involved in the regulation of capsular polysaccharide synthesis. In addition, mutations in the E. coli lon gene suppress temperature-sensitive mutations in other genes. The lon gene of Borrelia burgdorferi, encoding a homolog of the Lon protease, has been cloned and sequenced. The gene encodes a protein of 806 amino acids. The deduced amino acid sequence of the B. burgdorferi Lon protease shares substantial sequence identity with those of other known Lon proteases. The transcription start point of the B. burgdorferi lon gene was identified by primer extension analysis and the potential promoter did not show similarities to the consensus heat-shock promoter in E. coli. The 5'-end of the B. burgdorferi lon gene appears to suppress the temperature-sensitive phenotype of an E. coli lpxA mutant.

Borrelia burgdorferi uridine kinase: an enzyme of the pyrimidine salvage pathway for endogenous use of nucleotides

The 621 bp udk gene encoding Borrelia burgdorferi potential uridine kinase, involved in the pyrimidine salvage pathway, was cloned and sequenced. The B burgdorferi protein has a molecular mass of 24 kDa in sodium dodecyl sulfate-polyacrylamide gel. The N-terminal sequence of the protein, Ala-Lys-Ile-Ile, is identical to that predicted but lacks N-terminal methionine. udk is located at around 15 kb from the left telomere and forms an operon with an upstream ORF. A likely hypothesis for the role of the pyrimidine salvage pathway is the sole use of endogenous nucleotides for Borrelia.

Glycolytic enzyme operon of Borrelia burgdorferi: characterization and evolutionary implications

The genes encoding three enzymes of the glycolytic pathway have been identified and sequenced completely in Borrelia burgdorferi sensu stricto and partially in B. hermsii. They are clustered on the chromosome into an operon with a single putative promoter and are arranged downstream of this promoter in the following order: gapdh (glyceraldehyde-3-phosphate dehydrogenase), pgk (phosphoglycerate kinase), and tpi (triosephosphate isomerase). gapdh and pgk are separated by 19 bp of intergenic sequence and pgk and tpi are separated by only 1 bp. Each of the three genes contains a putative RBS 6-7 bp upstream of each respective translational (ATG) start codon. The deduced protein encoded by gapdh consists of 335 amino acids (aa) with a predicted MW of 36,400, that of pgk is 393 aa (MW of 42,156) and that of tpi is 290 aa (MW of 27,683). The aa sequences of each of the three enzymes share 58.4% (GAPDH), 52.8% (PGK) and 46.1% (TPI) identity with respective enzymes from other prokaryotic organisms. Phylogenetic analyses based on these universal and conserved proteins support the hypothesis that spirochetes are an ancient and distinct eubacterial phylum.

Molecular cloning and characterization of Borrelia burgdorferi rpoB

Borrelia burgdorferi rpoB, the gene encoding the beta-subunit of RNA polymerase, has been cloned and sequenced. The full-length gene encodes a protein of 1154 amino acids with a calculated molecular mass of 129.8 kDa. The amino-acid sequence is 49% identical to the corresponding protein from Escherichia coli. B. burgdorferi rpoB is a component of a gene cluster, which includes rplJ, rplL and rpoC. A temperature-sensitive E. coli rpoB mutant could be complemented by introduction of the B. burgdorferi gene, indicating that the B. burgdorferi rpoB is expressed in E. coli and the beta-subunit can be assembled into functional holoenzyme. The wild-type amino-acid sequence of the B. burgdorferi beta-subunit is consistent with those of spontaneously arising rifampicin-resistant mutants of E. coli and Mycobacterium tuberculosis at certain critical residues. This suggests that the natural resistance of B. burgdorferi to rifampicin may be due to the primary amino-acid sequence of its beta-subunit.

Identification and mapping of a chromosomal gene cluster of Borrelia burgdorferi containing genes expressed in vivo

A clone containing a 6.4 kb Borrelia burgdorferi chromosomal DNA insert reacted only with sera from patients with Lyme disease and not with any normal human or rabbit sera. Restriction enzyme analysis indicated that this DNA fragment was located on the B. burgdorferi chromosomal map between rpoB and p22A; its direction of transcription was towards p22A. Sequence analysis suggests that LA006 encodes six proteins: three previously described immunodominant lipoproteins of the 39 kDa Bmp protein family, BmpA, BmpB and BmpC; a 51 kDa MgtE magnesium transporter protein; a 16 kDa protein kinase C inhibitor; and a 56 kDa protein with similarity to an uncharacterized Escherichia coli chromosomal open reading frame.

Borrelia burgdorferi possesses a collagenolytic activity

Lyme disease is a multisystemic disorder caused by Borrelia burgdorferi, an invasive spirochete. B. burgdorferi has a predilection for collagenous tissue and one major clinical manifestation of the disease is arthritis. We have identified a collagenolytic activity in B. burgdorferi detergent lysates using iodinated gelatin as well as iodinated pepsinized human collagen types II and IV as protein substrates. In addition, we describe several proteolytic activities in B. burgdorferi with molecular masses greater than 200 kDa on sodium dodecyl sulfate polyacrylamide gels containing copolymerized gelatin. We propose that the collagenolytic activity of B. burgdorferi has a role in invasion, in the pathogenesis of Lyme arthritis, and perhaps also in other manifestations of Lyme borreliosis.

Binding of human urokinase type plasminogen activator and plasminogen to Borrelia species

Borrelia burgdorferi binds human urokinase plasminogen activator (uPA), which cleaves plasminogen (Pgn) to plasmin. The ability of other Borrelia species to bind uPA, Pgn, or both was investigated. Borrelia coriacae, Borrelia garinii, Borrelia parkeri, Borrelia anserina, and Borrelia turicatae were compared with infectious and noninfectious B. burgdorferi isolates. All Borrelia species lacked endogenous proteases capable of digesting casein, but all species bound human uPA and Pgn, generating Pgn-dependent proteolytic activity. There were no significant differences in the amount of plasmin, Pgn, or uPA bound per spirochete of the different species. On unfixed borreliae, fluorochrome-conjugated uPA bound to all species. Early binding was at the terminus of B. burgdorferi, whereas diffuse binding was observed on B. coriacae, B. garinii, B. parkeri, and B. turicatae. These studies demonstrate that binding of human uPA and Pgn to borreliae occurs on multiple species with apparent differences in surface distribution.

Inhibition of Borrelia burgdorferi-bound fibrinolytic enzymes by alpha2-antiplasmin, PAI-1 and PAI-2

Lyme disease is caused by Borrelia burgdorferi. Human plasminogen and urokinase-type plasminogen activator bind to the surface of the spirochete where plasmin is generated. We have suggested that bound urokinase and plasminogen are utilized by the organism to disseminate. We tested whether the physiological inhibitors of urokinase, plasminogen activator inhibitor-1 and -2 (PAI-1, PAI-2), could regulate the activity of spirochete-bound urokinase. The k(ass) of PAI-1 and PAI-2 for bound urokinase were 1.3 x 10(6) M(-1)s(-1) and 6.9 x 10(4)M(-1)s(-1), respectively, whereas the k(ass) for free urokinase were 7.2 x 10(6) M(-1)s(-1) and 5.3 x 10(5) M(-1)s(-1), respectively. Plasmin associated with the spirochete was not inhibited by alpha2-antiplasmin. These results suggest that PAI-1, PAI-2 and alpha2 antiplasmin would not be efficient regulators of fibrinolytic protease activity on the Borrelial surface and would not pose a barrier to utilization of these enzymes for dissemination in the human host.

Microbial genes homologous to the peptidyl-tRNA hydrolase-encoding gene of Escherichia coli

We have cloned and determined the nucleotide (nt) sequences of the genes encoding peptidyl-tRNA hydrolase (Pth) homologues of Salmonella typhi (St) and the Lyme disease spirochaete, Borrelia burgdorferi (Bb). We also completed the nt sequence of a pth homologous gene contained in a Chlamydia trachomatis (Ct) clone identified in the databanks. The open reading frames (ORFs) of the Pth homologues encode putative polypeptides of 194 (St), 188 (Bb) and 194 (Ct) amino acids exhibiting significant identity with Escherichia coli (Ec) Pth. Together with the products of two previously unidentified ORFs from Bacillus subtilis and Saccharomyces cerevisiae, and the recently recognized Haemophilus influenzae and Mycoplasma genitalium pth genes, these seven putative polypeptides and the Ec Pth form a group of homologous basic proteins spanning eubacteria and eukaryota which can be defined by at least three conserved regions. Previously known Ec pth mutations were located in highly conserved residues.

Analysis of the genetic polymorphism of Borrelia burgdorferi sensu lato by multilocus enzyme electrophoresis

In recent years, Borrelia burgdorferi sensu lato has been subdivided into three species, Borrelia burgdorferi sensu stricto, Borrelia garinii, and Borrelia afzelii, and a new species restricted to Japan, Borrelia japonica, has been isolated from Ixodes ovatus. In addition, members of several new genomic groups have been found in America and in Europe, suggesting that there are additional genospecies. In order to study the diversity of B. burgdorferi sensu lato, we analyzed 54 isolates, cultured from humans and from different tick species and obtained from diverse geographic areas, including Europe, the United States, Japan, and the People's Republic of China. In order to investigate the genetic relationship between microorganisms that are transmitted by soft ticks and microorganisms that cause Lyme disease, we also included three strains of relapsing fever spirochetes. The method which we used was multilocus enzyme electrophoresis; 12 genetic loci were characterized on the basis of the electrophoretic mobilities of their products, and 50 distinct allele profiles (electrophoretic types) were distinguished. The mean genetic diversity per locus was 0.747. a cluster analysis of a matrix of genetic distances for pairs of electrophoretic types revealed 11 divisions that were separated at genetic distances greater than 0.65. Five of these divisions corresponded to B. burgdorferi sensu stricto, B. garinii, B. afzelii, B. japonica, and the newly proposed species "Borrelia andersonii." Our results also confirmed that there are two additional genomic groups in Europe and at least one additional group in the United States. The relapsing fever spirochetes were were not clearly separated from the spirochetes associated with Lyme disease. In conclusion, we believe that the previously proposed subdivision of B. burgdorferi sensu lato into only four species should be reconsidered.

A glyceraldehyde-3-phosphate dehydrogenase homolog in Borrelia burgdorferi and Borrelia hermsii

A polyreactive monoclonal antibody recognized a 38.5-kDa polypeptide with amino-terminal sequence identity to conserved regions of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in Borrelia burgdorferi, the Lyme disease agent, and Borrelia hermsii, an agent of American relapsing fever. This monoclonal antibody also recognized GAPDH from other pathogenic spirochetes and other prokaryotes and eukaryotes as well. GAPDH activity was detected in sonicates of both B. burgdorferi and B. hermsii but not in live, intact organisms, indicating the possibility of a subsurface localization for the Borrelia GAPDH activity. Degenerate primers constructed from highly conserved regions of gapdh of other prokaryotes successfully amplified this gene homolog in both B. burgdorferi and B. hermsii. Nuclei acid and deduced amino acid sequence analysis of the 838-bp probes for each borrelia indicated 93.9% identity between B. burgdorferi and B. hermsii at the amino acid level. Amino acid identities of B. burgdorferi and B. hermsii with Bacillus stearothermophilus were 59.2% and 58.8% respectively. Southern hybridization studies indicated that the gene encoding GAPDH is located on the chromosome of each borrella. In other bacterial species, GAPDH has other functions in addition to its traditional enzymatic role in the glycolytic pathway. GAPDH may play a similar role in borrelias.

Association between different clinical manifestations of Lyme disease and different species of Borrelia burgdorferi sensu lato

Borrelia burgdorferi sensu lato, the aetiological agent of Lyme disease, has been subdivided into three species: B. burgdorferi sensu stricto, B. garinii and B. afzelii. We and other authors have hypothesized an association between the three species of B. burgdorferi sensu lato and some of the different clinical manifestations of Lyme disease. In order to demonstrate this hypothesis, we analysed twenty-nine isolates cultured from patients with different symptoms. The method used was multilocus enzyme electrophoresis: twelve genetic loci were characterized on the basis of the electrophoretic mobility of their products, and twenty-eight distinctive allele profiles (electrophoretic types) were distinguished, among which mean genetic diversity per locus was 0.649. Cluster analysis of a matrix of genetic distances between paired electrophoretic types revealed three primary divisions separated at genetic distances greater than 0.7 and corresponding to the three species of B. burgdorferi sensu lato. Ten strains obtained from skin of patients with erythema chronicum migrans (the primary stage of the disease) were assigned to the three different species. All the six strains isolated from patients with acrodermatitis chronica atrophicans were of the species B. afzelii, which was not found to be associated with another chronic manifestation of Lyme disease. Arthritis was caused prevalently by B. burgdorferi sensu stricto, and neuroborreliosis by B. burgdorferi sensu stricto and B. garinii. In conclusion, our results confirm the association between some of the different chronic manifestations of the disease and the species of B. burgdorferi sensu lato.

Comparative study of the enzyme activities of Borrelia burgdorferi and other non-intestinal and intestinal spirochaetes

Comparative analysis of the enzymatic profiles of 58 spirochaetal isolates clearly differentiated borrelias from leptospires, serpulinas and a treponeme. Strains of both Borrelia burgdorferi and Borrelia hermsii characteristically produced significant amounts of leucine arylamidase. This enzyme activity was not unique to borrelias but was also detected amongst pathogenic and non-pathogenic leptospira serovars. This fact, however, did not hamper a correct differentiation of borrelias from these spirochaetes, because leptospires possessed unique enzyme profiles. The API ZYM system could not differentiate the human strains of B. burgdorferi from those isolated from ticks, or from B. hermsii. Treponema phagedenis could be differentiated from all the other spirochaetes by the production of alpha-fucosidase. Our results confirm and extend previous studies indicating that human and animal intestinal spirochaetes have many common enzyme activities. All strains produced reactions of maximum intensity when tested for the presence of beta-galactosidase activity. However the avian strains lacked esterase (C4) which was present in human and swine intestinal spirochaetes. All strains of Serpulina hyodysenteriae, and Serpulina innocens as well as the human intestinal spirochaete strain HRM-14 showed alpha and beta glucosidase activity. Both enzyme activities were absent or insignificant in most other intestinal spirochaetes examined: 25 different human strains, non-pathogenic swine strain M1 and the avian strain 4742. However, swine strain LL3 and avian strain 1380 showed some beta-glucosidase activity.

Isolation and partial characterization of Borrelia burgdorferi inner and outer membranes by using isopycnic centrifugation

In order to characterize the protein composition of the outer membrane of Borrelia burgdorferi, we have isolated inner and outer membranes by using discontinuous sucrose density step gradients. Outer and inner membrane fractions isolated by this method contained less than 1 and 2%, respectively, of the total lactate dehydrogenase activity (soluble marker) in cell lysate. More importantly, the purified outer membranes contained less than 4% contamination by the C subunit of F1/F0 ATPase (inner membrane marker). Very little flagellin protein was present in the outer membrane sample. This indicated that the outer membranes were relatively free of contamination by cytoplasmic, inner membrane or flagellar components. The outer membrane fractions (rho = 1.19 g/cm3) contained 0.15 mg (dry weight) of protein per mg. Inner membrane samples (rho = 1.12 g/cm3) contained 0.60 mg (dry weight) of protein per mg. Freeze-fracture electron microscopy revealed that the outer membrane vesicles contained about 1,700 intramembranous particles per micron 2 while inner membrane densities for inner and outer membranes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and nonequilibrium pH gel electrophoresis-SDS-PAGE analyses of inner and outer membrane samples revealed several proteins unique to the inner membrane and 20 proteins that localized specifically to the outer membrane. This analysis clearly shows that the inner and outer membranes isolated by this technique are unique structures.

Genetic transformation of the Lyme disease agent Borrelia burgdorferi with coumarin-resistant gyrB

No useful method to genetically manipulate Borrelia burgdorferi, the causative agent of Lyme disease, has been developed previously. We have used resistance to the coumarin antibiotic coumermycin A1, an inhibitor of DNA gyrase, as a genetic marker to monitor the transformation of B. burgdorferi by electroporation. Introduction of site-directed mutations into the gyrB gene demonstrated that transformation was successful, provided evidence that homologous recombination occurs on the chromosome, and established that mutations at Arg-133 of DNA gyrase B confer coumermycin A1 resistance in B. burgdorferi. The coumermycin A1-resistant gyrB marker and genetic transformation can now be applied toward dissecting the physiology and pathogenesis of the Lyme disease agent on a molecular genetic level.

Genetic approaches to cell biology and metabolism of spirochetes

Genetic analysis and methodology have only comparatively recently been applied to the study of spirochetes. Although genetic transfer procedures for spirochetes are not widely available, there are several examples of progress in genetic analysis of spirochetes by other approaches. Some examples of these approaches are the following. 1) Genes for synthetic pathways in Treponema and Leptospira have been cloned by complementation of Escherichia coli serving as plasmid hosts. 2) The OspA protein of Borrelia burgdorferi has been overexpressed in E. coli without the signal peptide; the recombinant product has been suitable for circular dichroism as well as other biochemical analyses. 3) The heat shock proteins of B. burgdorferi are homologous to heat shock proteins of E. coli. 4) Enzyme activity profiles of B. burgdorferi and other spirochetes show strain heterogeneity and also indicate which biosynthetic and enzymatic activities are conserved within different spirochetes. 5) The gene organization of rRNA genes have revealed differences between spirochetes and other types of bacteria.

Characterization of Borrelia burgdorferi glycoconjugates and surface carbohydrates

Borrelia burgdorferi glycoconjugates with different oligosaccharide structures were characterized by a blotting technique with peroxidase-labelled lectins. The localization of surface carbohydrates was studied using electron microscopy with lectin-gold complexes. A high-mannose glycan structure was detected in 83 kDa glycoprotein (major extracellular protein); at least four carbohydrates (glucose or mannose, galactose, N-acetylgalactosamine and N-acetylglucosamine) were present in other Borrelia glycoconjugates. N-acetylneuraminic (sialic) acid was detected on the Borrelia surface. Two sialidases with different specificities were used in an attempt to cleave off the Borrelia N-acetylneuraminic acid. The attempt was successful by using Vibrio cholerae sialidase which has a broad substrate specificity, while the mumps-virus sialidase with restricted substrate specificity had no effect. Endogenous activity of N-acetylneuraminidase was not demonstrated in B. burgdorferi K 5 and B 31 strains.

Population genetic analysis of Borrelia burgdorferi isolates by multilocus enzyme electrophoresis

Fifty Borellia burgdorferi strains isolated from humans and ticks in Europe and the United States were analyzed by multilocus enzyme electrophoresis. Eleven genetic loci were characterized on the basis of the electrophoretic mobilities of their products. Ten loci were polymorphic. The average number of alleles per locus was 5.9, with a mean genetic diversity of 0.673 among electrophoretic types (ETs). The strains were grouped into 35 ETs constituting three main divisions (I, II, and III) separated at a genetic distance greater than 0.75. Divisions I, II, and III contained 13, 6, and 16 ETs, respectively. These findings, together with previous data from DNA hybridization and restriction enzyme analysis of rRNA genes, suggest that divisions I, II, and III may represent three distinct genomic species. All three divisions contained human clinical ETs. However, in division I, which includes the ET of the type strain of B. burgdorferi, the human pathogenic ETs constituted a single clone. The ETs of division I were from west-central Europe and the United States, whereas divisions II and III contained ETs from west-central and northern Europe but not from the United States. Finally, our data show that the genetic structure of B. burgdorferi populations is clonal.