Experimental gonococcal urethritis and reinfection with homologous gonococci in male volunteers

BACKGROUND

Reinfection, a common occurrence with gonorrhea, may result from a lack of protective immune response, or from the tremendous gonococcal strain variation.

GOAL

A two-phase study in human volunteers tested whether experimental infection with Neisseria gonorrhoeae MS11mkC would protect against reinfection with the same organisms.

STUDY DESIGN

In phase 1, an intraurethral inoculum of 57,000 piliated, transparent (opacity protein-negative [Opa-]) MS11mkC N gonorrhoeae infected 14 of 15 (93%) volunteers. The volunteers were encouraged to delay treatment for at least 5 days. In phase 2, which began 2 weeks after treatment for the initial infection, volunteers were inoculated with 7,100 piliated, Opa- MS11mkC.

RESULTS

The phase 2 challenge infected 6 of 14 (43%) previously infected volunteers and 5 of 10 (50%) naïve control subjects. Phase 1 volunteers who resisted reinfection were significantly more likely to have had a fourfold or greater increase in lipooligosaccharide immunoglobulin G during phase 1 than those who did not resist reinfection (P = 0.026).

CONCLUSIONS

Although infection did not provide protection from reinfection under the conditions used, the results suggest that immunity to reinfection is more complex than anticipated by the experimental design.

Neisseria gonorrhoeae MS11mkC opacity protein expression in vitro and during human volunteer infectivity studies

BACKGROUND AND OBJECTIVES

Neisseria gonorrhoeae MS11mkC harbors 11 independently expressed opacity (Opa) protein genes with distinct in vitro expression frequencies. In experimental infections in which human male volunteers were inoculated with transparent (Opa), piliated (P+) strains, the authors associate onset of symptoms with recovery of opaque (Opa+) gonococci.

GOALS

In vitro and recovered (Opa) protein expression rates were compared to determine if the human host influences Opa expression.

STUDY DESIGN

Opa expression was determined using Western immunoblot analysis; Opa sizes were determined using a scanning densitometer.

RESULTS

Seven of 10 Opa proteins were identified in gonococci recovered from all of the volunteers at frequencies consistent with in vitro results (Opa C, 29.5 kDa; Opa K, 30 kDa; Opa G, 31 kDa; Opa I, 32 kDa; Opa J, 33 kDa; Opa D, 34 kDa; and Opa H, 37 kDa) (P > or = 0.01, Fisher exact test). Opa B (30.5 kDa) was identified at lower than expected frequencies, whereas Opa E (31.2) and F (31.5) were identified at higher' than expected frequencies. When recovered gonococci were reanalyzed for in vitro expression frequencies, they were consistent with preinfection frequencies.

CONCLUSIONS

The host may influence the prevalence of some Opa proteins.

A typing system for neisseria gonorrhoeae based on biotinylated oligonucleotide probes to PIB gene variable regions

The porin proteins PIA and PIB of Neisseria gonorrhoeae are serotyping antigens for the serovar classification system and leading candidates for gonococcal vaccine development. Although serotyping has been a useful tool, this method can be insensitive to critical sequence changes in the por gene, including those in surface-exposed variable regions (VRs). A sensitive and specific typing system for N. gonorrhoeae has been developed that uses biotin-labeled oligonucleotide probes with chemiluminescence detection to type PIB gene VRs. The PIB VR types of geographically and temporally diverse gonococcal strains and sexual contact isolates were determined. por VR typing discriminated between most unrelated isolates and provided information about individual VR type that was not apparent from serovar designations. PIB VR typing avoids limited monoclonal antibody availability, interlaboratory variation, and the requirement for culture-based surveillance associated with gonococcal serotyping, and provides useful information about the molecular epidemiology of individual por gene VRs.

Linear epitopes of colonization factor antigen I and peptide vaccine approach to enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) cause diarrhea in infants and in travelers to developing countries. The bacteria utilize colonization factors (CF) for adherence to intestinal epithelia, then release toxins causing diarrhea. CF are strong immunogens as well as protective antigens. While 20 ETEC CF have been described in the literature, 11 CF are prominent enough to be considered for vaccine targeting. Of this group, six of the members fall into the CFA/I family of CF. Geysen pin (peptide) linear epitope analysis demonstrated that three regions containing linear epitopes exist in CFA/I, and that both B- and T-cell linear epitopes of CFA/I were concentrated at the N-terminus of the protein. We have determined N-terminal sequence of the CFA/I family members not previously sequenced. Comparison of the protein sequence of the six members of the family showed a strong homology up to residue 36. A peptide of 36 amino acids representing a consensus of the six sequences was synthesized and used to immunize animals. The antibody induced to the peptide was reactive to the peptide as well as cross-reactive to each member of the CFA/I family in Western blots. In addition, this antibody agglutinated three of the six members of the CFA/I family when added to whole cells expressing the native CF. We are currently evaluating different carriers and conjugation methods to maximize production of high titer, agglutinating antibody. It is hoped that this and related research will result in an effective and inexpensive cross-reactive and cross-protective ETEC vaccine.

Sialylation lessens the infectivity of Neisseria gonorrhoeae MS11mkC

In a human challenge experiment, the infectivity of gonococci with sialylated lipooligosaccharide (LOS) was compared with the infectivity of gonococci with unsialylated LOS. Volunteers were intraurethrally inoculated with approximately 5000 sialylated or unsialylated piliated, non-opaque (P+Opa-, transparent) colony type gonococci, strain MS11mkC. Five (83%) of 6 volunteers inoculated with unsialylated gonococci became infected; however, only 1 of 5 volunteers became infected with sialylated gonococci. The unsialylated gonococcal infections, with a median incubation time of 62 h (range, 32-98), were similar to previously described experimental infections. Gonococci shed by infected volunteers showed a transition from the P+Opa- phenotype of the inoculation strain to the P+Opa+ (piliated, opaque) phenotype 12-60 h before onset of disease. The subject with sialylated gonococcus infection had an extended incubation period, showing a progressive increase in the number of organisms shed until he became symptomatic on day 6 after inoculation. These results show that gonococci with sialylated LOS are less infective than gonococci with unsialylated LOS.

Assembly and antigenicity of the Neisseria gonorrhoeae pilus mapped with antibodies

The relationship between the sequence of Neisseria gonorrhoeae pilin and its quaternary assembly into pilus fibers was studied with a set of site-directed antibody probes and by mapping the specificities of antipilus antisera with peptides. Buried and exposed peptides in assembled pili were identified by competitive immunoassays and immunoelectron microscopy with polyclonal antibodies raised against 11 peptides spanning the pilin sequence. Pili did not compete significantly with pilin subunits for binding to antibodies against residues 13 to 31 (13-31) and 18-36. Pilus fibers competed well with pilin protein subunits for binding to antibodies raised against peptides 37-56, 58-78, 110-120, 115-127, 122-139, and 140-159 and competed weakly for antibodies against residues 79-93 and 94-108. Antibodies to sequence-conserved residues 37-56 and to semiconserved residues 94-108 preferentially bound pilus ends as shown by immunoelectron microscopy. The exposure of pilus regions to the immune system was tested by peptide mapping of antiserum specificities against sets of overlapping peptides representing all possible hexameric or octameric peptides from the N. gonorrhoeae MS11 pilin sequence. The immunogenicity of exposed peptides incorporating semiconserved residues 49-56 and 121-126 was revealed by strong, consistent antigenic reactivity to these regions measured in antipilus sera from rabbits, mice, and human and in sera from human volunteers with gonorrhea. The conservation and variation of antigenic responses among these three species clarify the relevance of immunological studies of other species to the human immune response against pathogens. Overall, our results explain the extreme conservation of the entire N-terminal one-third of the pilin protein by its dominant role in pilus assembly: hydrophobic residues 1-36 are implicated in buried lateral contacts, and polar residues 37-56 are implicated in longitudinal contacts within the pilus fiber.

Humoral responses to linear epitopes on the HIV-1 envelope in seropositive volunteers after vaccine therapy with rgp160

Humoral responses to the HIV-1 envelope were investigated in 30 human volunteers enrolled in a phase I vaccine therapy trial of rgp160 (LAI/LAV) using two techniques that emphasize detection of antibody response against linear (continuous) epitopes: immunoblotting and PEPSCAN. Seven fusion proteins containing large portions from constant regions 1, 2, 3, and 5, and variable region 3 of gp120 and two regions in the transmembrane protein, gp41, were employed in immunoblots to quantitatively measure immune response as a function of immunization. In addition, the entire gp160 (LAI/LAV) envelope protein was constructed in duplicate sets of 211 overlapping 12-mer peptides to fine-map the changes. Immunoblotting defined significant changes in reactivity to epitopes in constant regions; of 28 volunteers completing the trial, the percentage with reactivity against C1 changed from 62 to 100%; for C2, from 0 to 46%; for C3, from 0 to 82%; and for a constant region in gp41, from 25 to 68%. PEPSCAN on a subset (n = 8) of these volunteers identified new reactivity to epitopes throughout the envelope, concentrated in V1, C3, and C5 in gp120 and several peptides in gp41. Completely immunized patients responded to double the number of linear epitopes compared with two patients receiving alum alone. The results verify that the response to rgp160 is significantly broadened after immunization, providing additional evidence that HIV-1-infected volunteers can expand their antibody repertoire against a protein from a pathogen during chronic infection with that same pathogen. These results expand those previously obtained in this patient cohort, by defining explicitly the immunogenic regions recognized postvaccination and by providing methodology for quantitating those changes.

Experimental human gonococcal urethritis: 250 Neisseria gonorrhoeae MS11mkC are infective

Neisseria gonorrhoeae MS11mkA (mkA) expresses one 3.6-kDa lipooligosaccharide (LOS). Variant MS11mkC (mkC), expressing four larger LOSs, occurs in vitro among mkA at a frequency of 10(-3). Infectivity of these variants was compared in 2 groups of volunteers inoculated with approximately 40,000 piliated, Opa- gonococci of either strain. The mkC variant infected 5 of 5 while mkA infected only 2 (40%) of 5. Gonococci recovered from the mkA infections showed a transition toward the mkC LOS phenotype. The mkA inoculum contained approximately 40 mkC gonococci. These data confirmed earlier studies and suggested that small numbers of mkC gonococci would be infective. This hypothesis was tested in three more experiments. In two, volunteers were inoculated with 250 or 1250 mkC, infecting 3 of 7 in each group, and in the third, 1600 mkC infected 2 of 6, resulting in a total of 8 of 20 infected by < or = 1600 mkC. Gonococci shed by infected volunteers maintained the mkC LOS phenotype but shifted from Opa- to Opa+. Thus, LOS and opacity protein, as well as pilus, are gonococcal virulence factors.

Inflammatory cytokines produced in response to experimental human gonorrhea

Inflammatory cytokine production in men was examined after intraurethral challenge of volunteers with Neisseria gonorrhoeae MS11mkA or MS11mkC. Increased interleukin (IL)-8, IL-6, and tumor necrosis factor-alpha (TNF-alpha) were detected in urine before the onset of symptoms and peaked simultaneously with the detection of IL-1 beta at the onset of symptoms. Urine cytokine levels returned to baseline or near baseline within 48 h after antibiotic therapy. In plasma, IL-8, TNF-alpha, IL-1 beta, and IL-6 were elevated at the onset of symptoms in 9, 5, 4, and 3 of 10 subjects, respectively, and returned to near normal within 48 h after treatment. IL-1 alpha and granulocyte-macrophage colony-stimulating factor were not consistently detected in urine or plasma after challenge. Cytokine mRNA transcripts in peripheral blood mononuclear cells were not altered by the infection. The findings suggest that IL-8, IL-6, and possibly TNF-alpha were produced at the local site of infection, whereas IL-1 beta was derived from infiltrating leukocytes.

A mutation in the Neisseria gonorrhoeae rfaD homolog results in altered lipooligosaccharide expression

The gonococcal lsi-6 locus was cloned and shown by DNA sequence analysis to have homology with the E. coli rfaD gene, which encodes ADP-L-glycero-D-mannoheptose epimerase. This enzyme is involved in the biosynthesis of the lipopolysaccharide precursor ADP-L-glycero-D-mannoheptose. A site-directed frameshift mutation in lsi-6 was constructed by PCR amplification and introduced into the chromosome of Neisseria gonorrhoeae MS11 P+ by transformation. The lipooligosaccharides (LOS) of mutant and parental strains were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The lsi-6 mutant produced LOS components with apparent molecular masses of 2.6 and 3.6 kDa as compared with a 3.6-kDa band of the MS11 P+ strain. The parental LOS phenotype was expressed when a revertant was constructed by transformation of the cloned wild-type gene into the lsi-6 mutant. The immunoreactivity of LOS from parental and constructed strains was examined by SDS-PAGE and Western blotting. Only the parental and reconstructed wild-type strains produced a 3.6-kDa LOS component that reacted with monoclonal antibody 2-1-L8. These results suggest that the lsi-6 locus is involved in gonococcal LOS biosynthesis and that the nonreactive mutant 3.6-kDa LOS component contains a conformational change or altered saccharide composition that interferes with immunoreactivity.

Induction of humoral immune response against Plasmodium falciparum sporozoites by immunization with a synthetic peptide mimotope whose sequence was derived from screening a filamentous phage epitope library

The mouse monoclonal antibody 2A10 (immunoglobulin G), which recognizes the (NANP)n repeat of Plasmodium falciparum circumsporozoite surface protein, was used to screen a filamentous phage epitope library expressing random amino acid hexamers. The sequences obtained were TNRNPQ, SNRNPQ, NND-NPQ, SNYNPQ, and QNDNPQ (single-letter amino acid designation). These peptides showed 50% homology with the native epitope (PNANPN) and therefore were considered to mimic its structure (mimotopes). Two of these mimotopes (TNRNPQ and NNDNPQ) inhibited the binding of monoclonal antibody 2A10 to the recombinant protein R32LR, which contains the amino acid sequence [(NANP)15NVDP]2. Immunization of mice and rabbits using the peptide (TNRNPQ)4 induced a humoral response that recognized R32LR by an enzyme-linked immunosorbent assay and P. falciparum sporozoites by an immunofluorescence assay. These results suggest that phage epitope libraries can be exploited to screen for mimotopes in the design of subunit vaccines against infectious agents.

Plasmodium falciparum: further characterization of a functionally active region of the merozoite invasion ligand EBA-175

A 42 amino acid peptide, Pf EBA-175 (1062-1103), also called EBA-peptide 4 of the 175-kDa Plasmodium falciparum sialic acid binding protein, a putative merozoite invasion ligand, has been shown to be a target of parasite growth inhibitory antibodies. We expressed and purified a recombinant protein, NS1-Pf EBA-175 (946-1133) which included the 42 amino acid peptide, and compared antibodies induced by immunization with the protein to antibodies raised against the 42 amino acid peptide. Sera from rabbits immunized with the recombinant protein and the synthetic peptide immunoprecipitated authentic EBA-175, and had comparable ELISA titers against peptide Pf EBA-175 (1062-1103). However, IFAT titers against infected erythrocytes and growth inhibitory activity were substantially higher in sera from animals immunized with the 42 amino acid synthetic peptide. Epitope mapping of the 42 amino acid peptide identified a 19 amino acid peptide, Pf EBA-175 (1069-1087), which blocked the ability of antibodies against the 42 amino acid peptide to (1) immunoprecipitate EBA-175, (2) bind to the 42 amino acid peptide in an ELISA, and (3) recognize infected parasites in an IFAT. Sera from rabbits immunized with the 19 amino acid peptide conjugated to KLH had excellent parasite growth inhibitory activity (at 1:5 serum dilution, 49.9 +/- 7.4%, mean +/- SD of three separate assays), but the activity was lower in each of the three assays than that of sera from rabbits immunized with the 42 amino acid peptide (67.8 +/- 24.8%). These data indicate that the activity of antibodies raised against the linear 42 amino acid peptide, Pf EBA-175 (1062-1103) are primarily, if not exclusively, directed against 19 of the 42 amino acids, and identify this region of Pf EBA 175 as a target for vaccine development.

Differentiation of Pseudomonas aeruginosa pili based on sequence and B-cell epitope analyses

The nucleotide sequences of three previously undescribed Pseudomonas aeruginosa pilin structural genes are presented. Comparisons of deduced pilin primary structure and flanking DNA sequence allowed placement of these and six previously published sequences into one of two groups. Epitope mapping, using overlapping immobilized peptides representing the pilin primary structure, with antipilin monoclonal antibodies revealed several B-cell determinants grouped near the carboxyl terminus of P. aeruginosa 1244 pilin. One determinant was found to reside near the pilin constant region. These determinants were found associated with the pili of 31 of 95 P. aeruginosa clinical isolates.

Induction of cytolytic and antibody responses using Plasmodium falciparum repeatless circumsporozoite protein encapsulated in liposomes

Plasmodium circumsporozoite (CS) protein-induced antibody and T-cell responses are considered to be important in protective immunity. Since the key repeat determinant of the CS protein may actually restrict the recognition of other potential T- and B-cell sites, a modified Plasmodium falciparum CS protein lacking the central repeat region, RLF, was expressed in Escherichia coli. On purification, RLF was encapsulated into liposomes [L(RLF)] and used for the in vivo induction of cytolytic T lymphocytes (CTL) and antibodies. Immunization of B10.Br (H-2k) mice with L(RLF), but not with RLF, induced CD8+ CTL specific for the P. falciparum CS protein CTL epitope, amino acid residues 368-390. Anti-L(RLF) serum reacted with antigens on intact sporozoites and inhibited sporozoite invasion of hepatoma cells. Antibody specificity studies in New Zealand White rabbits revealed new B-cell sites localized in amino acid residues 84-94, 91-99, 97-106 and 367-375. Although the mechanisms by which liposomes enhance cellular and humoral immune responses remain unknown, liposome-formulated vaccines have been well tolerated in humans; hence, their use in vaccines, when efficacy depends on antibody and CTL responses, may be broadly applicable.

Analysis of Escherichia coli colonization factor antigen I linear B-cell epitopes, as determined by primate responses, following protein sequence verification

Colonization factor antigen I (CFA/I)-bearing strains of enterotoxigenic Escherichia coli (ETEC) are responsible for a significant percentage of ETEC diarrheal disease worldwide whether the disease presents as infant diarrhea with high mortality or as traveler's diarrhea. CFA/I pili (fimbriae) are virulence determinants that consist of repeating protein subunits (pilin), are found in several ETEC serogroups, and promote attachment to human intestinal mucosa. While CFA/I pili are highly immunogenic, the antigenic determinants of CFA/I have not been defined. We wished to identify the linear B-cell epitopes within the CFA/I molecule as determined by primate response to the immunizing protein. To do this, we (i) resolved the discrepancies in the literature on the complete amino acid sequence of CFA/I by N-terminal and internal protein sequencing of purified and selected proteolytic fragments of CFA/I, (ii) utilized this sequence to synthesize 140 overlapping octapeptides covalently attached to polyethylene pins which represented the entire CFA/I protein, (iii) immunized three rhesus monkeys with multiple intramuscular injections of purified CFA/I subunit in Freund's adjuvant, and (iv) tested serum from each monkey for its ability to recognize the octapeptides in a capture enzyme-linked immunosorbent assay. Eight linear B-cell epitopes were identified; the region containing an epitope at amino acids 11 to 21 was strongly recognized by all three individual rhesus monkeys, while the amino acid stretches 22 to 29, 66 to 74, 93 to 101, and 124 to 136 each contained an epitope that was recognized by two of the three rhesus monkeys. The three other regions containing epitopes were recognized by one of the three individuals. The monkey antiserum to pilus subunits recognized native intact pili by immunogold labeling of CFA/I pili present on whole H10407 cells. Therefore, immunization with pilus subunits induces antibody that clearly recognizes both synthetic linear epitopes and intact pili. We are currently studying the importance of these defined epitope-containing regions as vaccine candidates.

Human immunization with Pgh 3-2 gonococcal pilus results in cross-reactive antibody to the cyanogen bromide fragment-2 of pilin

In 1983, a gonococcal pilus vaccine failed to show protection in a large, placebo-controlled, double-blind field trial. The epitopic response to this vaccine was investigated in a random subgroup of 20 vaccine recipients. Using Western blot analysis of the immunizing pilus and its cyanogen bromide (CNBr) fragments, IgG antibody to pilin was detected before immunization in all individuals. Preexistent antibody to the CNBr-2 and CNBr-3 fragments of pilin was detected in 65% and 5% of individuals, respectively. Pilus immunization resulted in a vigorous response to the CNBr-2 fragment in 100% of the individuals tested; only 33% developed antibody to the CNBr-3 fragment. Absorptions of postimmunization sera with different gonococcal strains resulted in either complete or partial removal of antibody to the CNBr-2 fragment. In the context of an unsuccessful vaccine trial, these results suggest that antibody to the CNBr-2 fragment of pilin may not be protective.

Studies on the topography of the catalytic site of acetylcholinesterase using polyclonal and monoclonal antibodies

Polyclonal and monoclonal antibodies were generated against a synthetic peptide (25 amino acid residues) corresponding to the amino acid sequence surrounding the active site serine of Torpedo californica acetylcholinesterase (AChE). Prior to immunization, the peptide was either coupled to bovine serum albumin or encapsulated into liposomes containing lipid A as an adjuvant. To determine whether this region of AChE is located on the surface of the enzyme and thus accessible for binding to antibodies, or located in a pocket and thus not accessible to antibodies, the immunoreactivity of the antibodies was determined using enzyme-linked immunosorbent assay (ELISA), immunoprecipitation, Western blots, and competition ELISA. The polyclonal antibody and several of the monoclonal antibodies failed to react with either Torpedo or fetal bovine serum AChE in their native conformations, but showed significant cross-reactivity with the denatured enzymes. Human serum butyrylcholinesterase, which has a high degree of amino acid sequence homology with these AChEs, failed to react with the same antibodies in either native form or denatured form. Chymotrypsin also failed to react with the monoclonal antibodies in either form. Eighteen octapeptides spanning the entire sequence of this region were synthesized on polyethylene pins, and epitopes of representative monoclonal antibodies were determined by ELISA. The reactivity of peptides suggest that a portion of the 25 mer peptide in AChE containing the active site serine is the primary epitope. It is not exposed on the surface of the enzyme and is most likely sequestered in a pocket-like conformation in the native enzyme.

Lacto- and ganglio-series glycolipids are adhesion receptors for Neisseria gonorrhoeae

The role of glycolipids as adhesion receptors for Neisseria gonorrhoeae is examined. Serum-resistant isolates, piliated and nonpiliated isogenic variants, as well as gonococci deficient in lipooligosaccharide and protein II, bind specifically to terminal and internal GlcNAc beta 1-3Gal beta 1-4Glc and GalNAc beta 1-4Gal beta 1-4Gcl sequences in lacto- and ganglio-series glycolipids, respectively, as measured by overlaying glycolipid chromatograms with 125I-labeled organisms. The binding activity was not affected by changing the growth conditions of the organism, as the gonococci bound to both classes of glycolipids when grown anaerobically, microaerophilically on agar or in broth, or under iron-limited conditions. The gonococci do not bind to lacto-sylceramide (Gal beta 1-4Glc beta 1-1Cer) derived from lacto-N-triaosylceramide or from asialo-GM2 by treatment with N-acetyl-beta-hexosaminidase, or to other neutral glycolipids tested. Although N. gonorrhoeae bound weakly to some gangliosides on thin-layer chromatograms, including sialylparagloboside and GM1, in solid phase assays the gonococci bound with high avidity to the sequence GalNAc beta 1-4Gal beta 1-4Glc, with moderate avidity to the sequence GlcNAc beta 1-3Gal beta 1-4Glc, and not at all to gangliosides. Interestingly, the 4.8-kDa component of gonococcal lipooligosaccharide, which contains lacto-N-neotetraose (Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc), strongly inhibits gonococcal-specific agglutination of human erythrocytes and inhibits the binding of labeled organisms to human paragloboside and lacto-N-triaosylceramide on thin-layer chromatograms. Possibly, this binding specificity explains why gonococci autoagglutinate in vitro.

Complete amino acid sequence of fetal bovine serum acetylcholinesterase and its comparison in various regions with other cholinesterases

The complete amino acid sequence of a mammalian acetylcholinesterase from fetal bovine serum (FBS AChE) is presented. This enzyme has a high degree of sequence identity with other cholinesterases, liver carboxyesterases, esterase-6, lysophospholipase, and thyroglobulin. The locations of 191 amino acids in 10 regions of the FBS enzyme were compared with corresponding sequences of Torpedo, human, and Drosophila AChEs and human serum butyrylcholinesterase (BChE). In one region there is a marked difference in both the number of amino acids and their sequence between mammalian AChE and other AChEs and the human serum BChE. The amino acid sequence of FBS AChE showed overall homologies of 90% with human AChE, 60% with T. california AChE, 50% with human serum BChE, and 39% with Drosophila AChE in these regions.

Biochemical purification and crystallographic characterization of the fiber-forming protein pilin from Neisseria gonorrhoeae

Pilus fibers are long protein filaments on many pathogenic bacteria that participate in attachment to host cells. Although the self-assembling protein pilin is the major structural component of the Neisseria gonorrhoeae pilus fiber, several other proteins co-purified with pilin through the repeated solubilization-reassociation steps of the biochemical purification. Pilin solubilized in the nondenaturing detergent n-octyl-beta-D-glucopyranoside remained an aggregate of about 100 kDa at pH 9.5, but was reduced to a 40-kDa dimer at pH 10.5, suggesting that assembly involves electrostatic interactions of lysine, tyrosine, or other side chains with high pKa values. Pilin dimers and aggregates of higher molecular mass were partially stable even in the presence of sodium dodecyl sulfate and beta-mercaptoethanol. Removal of pilus-associated proteins and stabilization of pilin multimers permitted the reproducible crystallization of pilin. Three-dimensional needle- and plate-shaped crystals of purified N. gonorrhoeae pilin (strain MS11 variant C30) grew from 36 to 40% polyethylene glycol 400, pH 8.0-9.0, in space group C222, with cell dimensions a = 126.4, b = 121.2, c = 26.7 A and Vm = 2.84 A3/dalton for one molecule per asymmetric unit. The best crystals diffracted to 2.4 A resolution using synchrotron radiation, were stable to x-ray damage, and appear suitable for determination of the atomic structure. This approach of stabilizing and crystallizing an intermediate assembly state may be useful for other fiber-forming proteins, which have previously not been successfully crystallized in forms that diffract to atomic resolution.

Pilin independent binding of Neisseria gonorrhoeae to immobilized glycolipids

The adherence process in pathogenesis involves the attachment of bacteria to structures present on eukaryotic cell surfaces. To investigate components necessary for this interaction, we have characterized the binding of N. gonorrhoeae to eukaryotic glycolipids immobilized on thin layer chromatograms. The gonococci specifically bind to a subset of glycolipids consisting of lactosylceramide, gangliotriosylceramide, and gangliotetraosylceramide. This binding was identified in both piliated and nonpiliated cells, and is postulated to be mediated by a nonpilin lectin-like adhesin protein.

Solubilization, isolation, and immunochemical characterization of the major outer membrane protein from Rhodopseudomonas sphaeroides

Solubilization of the major outer membrane protein of Rhodopseudomonas sphaeroides, and subsequent isolation, has been achieved by both non-detergent- and detergent-based methods. The protein was differentially solubilized from other outer membrane proteins in 5 M guanidine thiocyanate which was exchanged by dialysis for 7 M urea. The urea-soluble protein was purified to homogeneity by a combination of DEAE-Sephadex chromatography and preparative electrophoretic techniques. Similar to the peptidoglycan-associated proteins of other Gram-negative bacteria, the protein was also purified by differential temperature extraction of the outer membrane in the presence of sodium dodecyl sulfate (SDS) followed by preparative SDS-polyacrylamide gel electrophoresis. Immunochemical analysis of the proteins isolated by the two techniques established the immunochemical identity and homogeneity of each preparation. Immunoblots of SDS-polyacrylamide gels revealed that antibody directed against the major outer membrane protein reacted with the three high molecular weight aggregates present in the outer membrane which we have previously shown to be composed of the major outer membrane protein and three nonidentical small molecular weight proteins.

Physical and chemical characterization of the major outer membrane protein of Rhodopseudomonas sphaeroides

The characterization of the major outer membrane protein of Rhodopseudomonas sphaeroides is described. Molecular weight estimations using Ferguson plots derived from sodium dodecyl sulfate and urea-polyacrylamide gels were 39,500 and 32,200, respectively, in good agreement with the value of 33,800 obtained from amino acid compositional studies. NH2-terminal amino acid determinations of the major outer membrane protein revealed a blocked NH2 terminus. Gas chromatography of the acid-hydrolyzed protein confirmed the presence of fatty acid covalently associated with the protein presumably through an amino linkage. Peptide mapping of tryptic and chymotryptic digestions of the protein led to the identification of one peptide in each digest containing fatty acid. Digestion of the fatty acid-containing peptide with pronase resulted in the fatty acid together with L-alanine becoming extractable into hexane. We conclude that the major outer membrane protein of R. sphaeroides is a proteolipid containing at least 1 mol of fatty acid/mol of protein in amide linkage to the NH2-terminal L-alanine of the protein.

Immunochemical relationship of the major outer membrane protein of Rhodopseudomonas sphaeroides 2.4.1 to proteins of other photosynthetic bacteria

Immunoblots of sodium dodecyl sulfate-polyacrylamide gels derived from outer membrane preparations of various strains of Rhodopseudomonas sphaeroides revealed polypeptides which cross-reacted with antibody directed against the major outer membrane protein of R. sphaeroides 2.4.1. Immunochemical quantitation of the major outer membrane protein of strain 2.4.1 showed approximately 5.5 x 10(4) molecules per cell whether cells were grown chemoheterotrophically or photoheterotrophically. Rhodospirillum rubrum outer membranes contained a cross-reactive protein, whereas the outer membranes derived from Rhodopseudomonas capsulata and Paracoccus denitrificans showed no cross-reaction with the antibody prepared against the major outer membrane protein from R. sphaeroides 2.4.1.

In vivo intermembrane transfer of phospholipids in the photosynthetic bacterium Rhodopseudomonas sphaeroides

The kinetics of accumulation of phospholipids into the intracytoplasmic membrane of Rhodopseudomonas sphaeroides have been examined. We have previously demonstrated that accumulation of phospholipids in the intracytoplasmic membrane is discontinuous with respect to the cell cycle. In this study we demonstrated a sevenfold increase in the rate of phospholipid incorporation into the intracytoplasmic membrane concurrent with the onset of cell division. Pulse-chase labeling studies revealed that the increase in the rate of phospholipid accumulation into the intracytoplasmic membrane results from the transfer of phospholipid from a site other than the intracytoplasmic membrane, and that the transfer of phospholipid, rather than synthesis of phospholipid, is most likely subject to cell cycle-specific regulation. The rates of synthesis of the individual phospholipid species (phosphatidylethanolamine, phosphatidyglycerol, and an unknown phospholipid) remained constant with respect to one another throughout the cell cycle. Similarly, each of these phospholipid species appeared to be transferred simultaneously to the intracytoplasmic membrane. We also present preliminary kinetic evidence which suggested that phosphatidylethanolamine may be converted to phosphatidycholine within the intracytoplasmic membrane.