Insertion of N-Terminal Hinge Glycosylation Enhances Interactions of the Fc Region of Human IgG1 Monomers with Glycan-Dependent Receptors and Blocks Hemagglutination by the Influenza Virus

In therapeutic applications in which the Fc of IgG is critically important, the receptor binding and functional properties of the Fc are lost after deglycosylation or removal of the unique Asn297 N-X-(T/S) sequon. A population of Fcs bearing sialylated glycans has been identified as contributing to this functionality, and high levels of sialylation also lead to longer serum retention times advantageous for therapy. The efficacy of sialylated Fc has generated an incentive to modify the unique N-linked glycosylation site at Asn297, either through chemical and enzymatic methods or by mutagenesis of the Fc, that disrupts the protein-Asn297 carbohydrate interface. In this study, we took an alternative approach by inserting or deleting N-linked attachment sites into the body of the Fc to generate a portfolio of mutants with tailored effector functions. For example, we describe mutants with enhanced binding to low-affinity inhibitory human Fcγ and glycan receptors that may be usefully incorporated into existing Ab engineering approaches to treat or vaccinate against disease. The IgG1 Fc fragments containing complex sialylated glycans attached to the N-terminal Asn221 sequon bound influenza virus hemagglutinin and disrupted influenza A-mediated agglutination of human erythrocytes.

Involvement of Tyrosines at Fucose-binding Sites ofAleuria aurantiaLectin: Non-equal Response to Site-directed Mutagenesis among Five Sites

Since the involvement of Tyr residues in the fucose-binding of Aleuria aurantia lectin (AAL) was proved by chemical modification using the Tyr-specific reagent tetranitromethane, site-directed mutagenesis was attempted. Since the tertiary structure of AAL was determined recently to be a six-bladed beta-propeller fold, and five fucose-binding sites per subunit were found, based on positions of Tyr residues in the tertiary structure, three classes of mutants were constructed: 1) Tyr on the 2nd beta-strand of each blade (beta-2 mutants), 2) Tyr or Trp on the 3rd beta-strand (beta-3 mutants), and 3) Tyr outside of binding sites (other-Y mutants). The mutagenized cDNA was expressed in Escherichia coli as His-tag-AAL, and the hemagglutinating activity was assayed. Among 14 mutants, three beta-2 mutants (Y26A, Y79A, and Y181A), and three beta-3 mutants (Y92A, W149A, and Y241A) showed decreased activity. These mutated residues resided at Sites 1, 2, and 4, at the same locations relatively in the binding sites. Mutagenesis of Tyr or Trp at the corresponding locations in Sites 3 and 5 did not lead to a reduction in activity. Results indicate that the properties of Sites 1, 2, and 4 are different from those of Sites 3 and 5, and that the contribution of these two sites to the hemagglutination reaction was minor.

Quantitative assessment of Mycoplasma hemadsorption activity by flow cytometry

A number of adherent mycoplasmas have developed highly complex polar structures that are involved in diverse aspects of the biology of these microorganisms and play a key role as virulence factors by promoting adhesion to host cells in the first stages of infection. Attachment activity of mycoplasma cells has been traditionally investigated by determining their hemadsorption ability to red blood cells and it is a distinctive trait widely examined when characterizing the different mycoplasma species. Despite the fact that protocols to qualitatively determine the hemadsorption or hemagglutination of mycoplasmas are straightforward, current methods when investigating hemadsorption at the quantitative level are expensive and poorly reproducible. By using flow cytometry, we have developed a procedure to quantify rapidly and accurately the hemadsorption activity of mycoplasmas in the presence of SYBR Green I, a vital fluorochrome that stains nucleic acids, allowing to resolve erythrocyte and mycoplasma cells by their different size and fluorescence. This method is very reproducible and permits the kinetic analysis of the obtained data and a precise hemadsorption quantification based on standard binding parameters such as the dissociation constant K_d. The procedure we developed could be easily implemented in a standardized assay to test the hemadsorption activity of the growing number of clinical isolates and mutant strains of different mycoplasma species, providing valuable data about the virulence of these microorganisms.

A BCAM0223 mutant of Burkholderia cenocepacia is deficient in hemagglutination, serum resistance, adhesion to epithelial cells and virulence

Burkholderia cepacia complex (Bcc) bacteria are a problematic group of microorganisms causing severe infections in patients with Cystic Fibrosis. In early stages of infection, Bcc bacteria must be able to adhere to and colonize the respiratory epithelium. Although this is not fully understood, this primary stage of infection is believed to be in part mediated by a specific type of adhesins, named trimeric autotransporter adhesins (TAAs). These homotrimeric proteins exist on the surface of many gram negative pathogens and often mediate a number of critical functions, including biofilm formation, serum resistance and adherence to an invasion of host cells. We have previously identified in the genome of the epidemic clinical isolate B. cenocepacia J2315, a novel cluster of genes putatively encoding three TAAs (BCAM0219, BCAM0223 and BCAM0224). In this study, the genomic organization of the TAA cluster has been determined. To further address the direct role of the putative TAA BCAM0223 in B. cenocepacia pathogenicity, an isogenic mutant was constructed via insertional inactivation. The BCAM0223::Tp mutant is deficient in hemagglutination, affected in adherence to vitronectin and in biofilm formation and showed attenuated virulence in the Galleria mellonella model of infection. Moreover, the BCAM0223::Tp mutant also showed a significant reduction in its resistance to human serum as well as in adherence, but not in invasion of, cultured human bronchial epithelial cells. Altogether these results demonstrate that the BCAM0223 protein is a multifunctional virulence factor that may contribute to the pathogenicity of B. cenocepacia.

QseBC controls flagellar motility, fimbrial hemagglutination and intracellular virulence in fish pathogen Edwardsiella tarda

The inter-kingdom communication with the mammalian hosts mediated by autoinducer-3 (AI-3)/epinephrine (Epi)/norepinephrine (NE), and transduced by two-component systems QseBC has recently been described. As a fish pathogen and opportunistic pathogen for human beings, Edwardsiella tarda develops surface structures such as flagellar and fimbriae to cause different hemagglutination phenotypes and serotypes and initiate pathogen-host recognition and invasion process. E. tarda survives within macrophages in fish using type III secretion system (TTSS). Here, the genes of E. tarda two-component system, qseB and qseC, were found to be co-transcribed. Phylogenetic analysis indicated that evolution of QseC strongly correlated to different host niches. Compared with the wild type and their complemented strains, ΔqseB and ΔqseC mutants exhibited significant impaired flagellar motilities. Mammalian Epi was able to stimuli the flagellar motility in E. tarda via QseBC. Hemagglutination caused by fimbriae was induced in ΔqseB but repressed in ΔqseC. Disruption of qseB or qseC down-regulated the intracellular expressions of TTSS elements EseB and EsaC, and impaired their intracellular survival capabilities as well as in vivo competitive abilities. Furthermore, in vitro tests indicated that expression of EseB was induced by Epi via QseBC. Our results revealed that the QseBC system modified the virulence-related surface structures (flagellum, fimbriae and secretion system) and that hormone might stimulate the virulence of the pathogen in fish.

Biological and immunological relations among human parvovirus B19 genotypes 1 to 3

The human parvovirus B19 is now divided into three genotypes: type 1 (prototype), type 2 (A6- and LaLi-like), and type 3 (V9-like). In overall DNA sequence, the three virus types differ by approximately 10%. The most striking DNA dissimilarity, of >20%, is observed within the p6 promoter region. Because of the scarcity of data on the biological activities and pathogenetic potentials of virus types 2 and 3, we examined the functional characteristics of these virus types. We found the activities of the three p6 promoters to be of equal strength and to be most active in B19-permissive cells. Virus type 2 capsid protein VP2, alone or together with VP1, was expressed with the baculovirus system and was shown to assemble into icosahedral parvovirus-like particles, which were reactive in the hemagglutination assay. Furthermore, sera containing DNA of any of the three B19 types were shown to hemagglutinate. The infectivities of these sera were examined in two B19-permissive cell lines. Reverse transcription-PCR revealed synthesis of spliced B19 mRNAs, and immunofluorescence verified the production of NS and VP proteins in the infected cells. All three genotypes showed similar functional characteristics in all experiments performed, showing that the three virus types indeed belong to the same species, i.e., human parvovirus B19. Additionally, the antibody activity in sera from B19 type 1- or type 2-infected subjects (long-term immunity) was examined with homo- and heterologous virus-like particles. Cross-reactivity of 100% was observed, indicating that the two B19 genotypes comprise a single serotype.

Characterization of adhesin variants in Indian isolates of enteroaggregativeEscherichia coli

Enteroaggregative Escherichia coli (EAEC) are causative agents of diarrhea, being characterized by aggregative adherence to cultured epithelial cells. In this study, phenotypic properties of EAEC were analyzed with respect to AA, hemagglutination, clump and biofilm formation, all of which are mediated by aggregative adherence fimbriae (AAF). The strains were also screened for AAF types, AAF adhesin variants and Dr adhesin by PCR. Of the three known AAF types, AAF/I and AAF/II adhesin variants were identified. An association between the AAF/adhesin genotypes and the subtypes/scores of phenotypic properties was sought and it was observed that strains harboring same adhesins displayed different subtypes/scores and vice versa.

Altered glycosylation leads to Tr polyagglutination

BACKGROUND

Polyagglutination refers to red blood cells (RBCs) that are agglutinated by a high proportion of ABO-matched adult sera but not by cord sera. Polyagglutinable RBCs have been associated with microbial infection, myeloproliferative disorders, and myelodysplasia. Lectins aid in the identification of polyagglutination.

CASE STUDY

A Hispanic male infant with mild hemolytic anemia, a "Bernard-Soulier-like" syndrome, intermittent neutropenia, mitral valve regurgitation, ligament hyperlaxity, and mild mental retardation was studied. The patient's Group O RBCs were polyagglutinable; they were agglutinated by normal human sera, several lectins [including Arachis hypogea, Salvia sclarea, Salvia horminum, Glycine max, Ulex europaeus, Griffonia simplicifolia I, and Gr. simplicifolia II], and some monoclonal antibodies. His RBCs were not agglutinated by cord sera, Dolichos biflorus, or Phaseolus lunatus. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis on the RBC membranes followed by staining with periodic acid-Schiff stain showed markedly reduced staining of glycophorins A and B. Staining with Coomassie brilliant blue revealed that Band 3 has a faster mobility than normal.

CONCLUSIONS

Collectively, the results suggest that the patient's RBCs have a reduction in N-acetylneuraminic acid on both N- and O-glycans, exposing, respectively, beta1,4-galactosidase and beta1,3-galactosidase. The patient likely has an altered glycosyltransferase that results in defective glycosylation in RBCs and other cell lineages. This type of polyagglutination was named Tr.

Subcloning of the 200-kDa Porphyromonas gingivalis antigen gene and inhibition of hemagglutination by an antibody against the recombinant protein

Porphyromonas gingivalis is a major etiologic agent of periodontitis and exhibits hemagglutinating and adherence activities. We previously succeeded in molecular cloning the 200-kDa cell-surface antigenic protein (200-k AP), designated pMD101, that is recognized in sera from periodontitis patients, and identified the 200-k AP as a hemagglutinin A (HagA) derivative. HagA is one of the hemagglutinins known to be a useful vaccine against periodontitis. HagA has four large, contiguous, direct repeats and the repeat unit is believed to contain the hemagglutinin domain. Because production of 200-k AP was low in the Escherichia coli host, it was difficult to obtain large amounts of recombinant protein. In this study, we attempt to subclone the gene encoding the useful antigen from pMD101 in an effort to obtain large quantities. A subclone, designated pMD160, encoding a fusion protein of 80-kDa HagA and maltose-binding protein was successfully constructed, and the novel clone produced relatively large amounts of recombinant protein. DNA nucleotide sequences of the pMD160 insert demonstrated that the 80-kDa protein contained a short hemagglutinin motif and a direct repeat unit region. The recombinant protein was purified to homogeneity and rabbit antiserum was raised. The antibody was capable of inhibiting the hemagglutinating activity of P. gingivalis. These findings suggest that novel 80-kDa HagA derivative proteins can be produced efficiently from E. coli hosts and these may be useful in developing immunotherapy against periodontitis infected by P. gingivalis.

Red blood cell antigens responsible for inherited types of polyagglutination

The three described types on inheritable polyagglutination are related to altered carbohydrate structures in glycoproteins or/and glycolipds on the erythrocyte surface. HEMPAS, a condition causing anemia and other pathological symptoms, is characterized by impaired biosynthesis of N-glycans, mostly those carried by band 3 and band 4.5 erythrocyte membrane proteins. Cad erythrocytes have abnormal glycophorin O-glycans, structurally related to the more common human Sd(a) and murine CT determinants, and accumulate an Sd(a)-like ganglioside. NOR erythrocytes express recently detected abnormal alpha-galactose-terminated glycosphingolipids, which strongly react with G. simplicifolia IB4 isolectin, but do not react with human anti-Galalpha1-3Gal antibodies.

Immunotherapy of established tumors using bone marrow transplantation with antigen gene--modified hematopoietic stem cells

A major focus of cancer immunotherapy is to develop strategies to induce T-cell responses through presentation of tumor antigens by dendritic cells (DCs). Current vaccines are limited in their ability to efficiently transfer antigens to DCs in vivo. Ex vivo-generated DCs can be efficiently loaded with antigen but after reinjection, few DCs traffic to secondary lymphoid organs, the critical sites for antigen presentation. To enhance efficiency and durability of antigen presentation by DCs, we transduced hematopoietic stem-progenitor cells (HSCs) with a model tumor antigen and then transplanted the gene-modified cells into irradiated recipient mice, which resulted in efficient expression of the transgene in a large proportion of donor derived DCs in lymphoid organs. The combination of bone marrow transplantation (BMT) using transduced HSCs, systemic agents that generate and activate DCs, and mature T-cell infusion resulted in substantial expansion and activation of antigen-specific T cells. This tripartite strategy provided potent antigen-specific immunotherapy for an aggressive established tumor.

MlrA, a novel regulator of curli (AgF) and extracellular matrix synthesis by Escherichia coli and Salmonella enterica serovar Typhimurium

Production of curli (AgF) adhesins by Escherichia coli and Salmonella enterica serovar Typhimurium (S. typhimurium) is associated with extracellular matrix production and is optimal at low temperature during stationary phase. Curli and extracellular matrix synthesis involves a complex regulatory network that is dependent on the CsgD (AgfD) regulator. We have identified a novel regulator, termed MlrA, that is required for curli production and extracellular matrix formation. Two cosmids from a genomic library of avian pathogenic E. coli chi7122 conferred mannose-resistant haemagglutination (HA) and curli production to E. coli HB101, which is unable to produce curli owing to a defective regulatory pathway. The rpoS gene, encoding a known positive regulator of curli synthesis, and the E. coli open reading frame (ORF) of unknown function, yehV, identified on each of these cosmids, respectively, conferred curli production and HA to E. coli HB101. We have designated yehV as the mlrA gene for MerR-like regulator A because its product shares similarities with regulatory proteins of the MerR family. HA and curli production by strain chi7122 were abolished by disruption of rpoS, mlrA or csgA, the curli subunit gene. Both csgD and csgBA transcription, required for expression of curli, were inactive in an mlrA mutant grown under conditions that promote curli production. An mlrA homologue was identified in S. typhimurium. Analysis of mlrA-lac operon fusions demonstrated that mlrA was positively regulated by rpoS. mlrA mutants of wild-type S. typhimurium SL1344 or SR-11 no longer produced curli or rugose colony morphology, and exhibited enhanced aggregation and extracellular matrix formation when complemented with the mlrA gene from either S. typhimurium or E. coli present on a low-copy-number plasmid. However, inactivation of mlrA did not affect curli production and aggregative morphology in an upregulated curli producing S. typhimurium derivative containing a temperature- and RpoS-independent agfD promoter region. These results indicate that MlrA is a newly defined transcriptional regulator of csgD/agfD that acts as a positive regulator of RpoS-dependent curli and extracellular matrix production by E. coli and S. typhimurium.

Unique hemagglutination activity of an isolate of Newcastle disease virus

The MET95 strain of a lentogenic Newcastle disease virus (NDV) isolated from a broiler in Japan, showed unique hemagglutination (HA) activity. The MET95 strain failed to show HA when examined by rapid glass plate method although they showed HA titer of 1:1,024 by micro-plate method. This unique HA was also observed after the MET95 strain was passaged ten times in chickens. The failure of HA by rapid glass plate method was not shown in any other NDVs examined.

Evans antigen: a new hybrid structure occurring on background of D.. and D-- Rh complexes

BACKGROUND AND OBJECTIVES

Previously, the Evans antigen (RH37) of the Rh blood group system was shown to be specified by a novel CE-D-CE hybrid gene. We studied further the heterogeneity of Evans and report here its new molecular type resulting from a novel intraexon fusion event on the background of D. and D-- complexes.

MATERIALS AND METHODS

A white family with 2 Evans+ and 2 Evans- members was analyzed by serological methods and molecular techniques.

RESULTS

The Evans+ proband (JD) typed D+C-c-E-e- and showed a partial loss of RHCE but an increased dose of RHD on DNA blots. On sequencing of Rh cDNAs, a normal D and 3 hybrid transcripts were detected. The D-CE hybrid is characterized by a single breakpoint located in exon 6. The CE-D hybrid derived its exon 1 (or 1 and 2) from RHCE and exons 2-10 (or 3-10) from RHD. The CE-D-CE hybrid had its internal exons 2-7 (or 3-7) from RHD. Family studies showed that the D-CE and CE-D hybrids were linked and cotransmitted from JD to his son, whereas RHD and CE-D-CE hybrid were transmitted from JD to his daughter.

CONCLUSION

In this family, Evans is specified by the novel D-CE intraexon fusion gene which occurs in cis to CE-D and trans to CE-D-CE interexon fusion genes. The observed large duplication of RHD reflects a convergent mosaicism underlying the enhancement of D and ablation of CcEe antigens.

Characterization of the sialic acid binding activity of transmissible gastroenteritis coronavirus by analysis of haemagglutination-deficient mutants

Transmissible gastroenteritis coronavirus (TGEV) agglutinates erythrocytes of several species by virtue of sialic acid binding activity of the surface protein S. We have isolated and characterized five haemagglutination-defective (HAD) mutants. In contrast to the parental virus, the mutants were unable to bind to porcine submandibulary mucin, a substrate rich in sialic acid. Each of the mutants was found to contain a single point mutation in the S protein (Cys155Phe, Met195Val, Arg196Ser, Asp208Asn or Leu209Pro), indicating that these amino acids are affecting the sialic acid binding site. In four of the HAD mutants a nearby antigenic site is affected in addition to the sialic acid binding site, as indicated by reactivity with monoclonal antibodies. The parental virus was found to have an increased resistance to the detergent octylglucoside compared to the HAD mutants. This effect depended on cellular sialoglycoconjugates bound to the virion. If the binding of sialylated macromolecules was prevented by neuraminidase treatment, the parental virus was as sensitive to octylglucoside as were the HAD mutants. We discuss the possibility that the sialic acid binding activity helps TGEV to resist detergent-like substances encountered during the gastrointestinal passage and thus facilitates the infection of the intestinal epithelium. An alternative function of the sialic acid binding activity - accessory binding to intestinal tissues - is also discussed.

Bordetella avium virulence measured in vivo and in vitro

Bordetella avium causes an upper-respiratory-tract disease called bordetellosis in birds. Bordetellosis shares many of the clinical and histopathological features of disease caused in mammals by Bordetella pertussis and Bordetella bronchiseptica. In this study we determined several parameters of infection in the domestic turkey, Meleagris galapavo, and compared these in vivo findings with an in vitro measure of adherence using turkey tracheal rings. In the in vivo experiments, we determined the effects of age, group size, infection duration, and interindividual spread of B. avium. Also, the effect of host genetic background on susceptibility was tested in the five major commercial turkey lines by infecting each with the parental B. avium strain and three B. avium insertion mutants. The mutant strains lacked either motility, the ability to agglutinate guinea pig erythrocytes, or the ability to produce dermonecrotic toxin. The susceptibilities of 1-day-old and 1-week-old turkeys to B. avium were the same, and challenge group size (5, 8, or 10 birds) had no effect upon the 50% infectious dose. Two weeks between inoculation and tracheal culture was optimal, since an avirulent mutant (unable to produce dermonecrotic toxin) persisted for a shorter time. Communicability of the B. avium parental strain between confined birds was modest, but a nonmotile mutant was less able to spread between birds. There were no host-associated differences in susceptibility to the parental strain and the three B. avium mutant strains just mentioned: in all turkey lines tested, the dermonecrotic toxin- and hemagglutination-negative mutants were avirulent whereas the nonmotile mutants showed no loss of virulence. Interestingly, the ability of a strain to cause disease in vivo correlated completely with its ability to adhere to ciliated tracheal cells in vitro.

Identification of the Vibrio cholerae type 4 prepilin peptidase required for cholera toxin secretion and pilus formation

Cholera toxin secretion is dependent upon the extracellular protein secretion apparatus encoded by the eps gene locus of Vibrio cholerae. Although the eps gene locus encodes several type four prepilin-like proteins, the peptidase responsible for processing these proteins has not been identified. This report describes the identification of a prepilin peptidase from the V. cholerae genomic database by virtue of its homology with the PilD prepilin peptidase of Pseudomonas aeruginosa. Plasmid disruption or deletion of this peptidase gene in either EI Tor or classical V. cholerae O1 biotype strains results in a dramatic decrease in cholera toxin secretion. In the case of the EI Tor biotype mutants, surface expression of the type 4 pilus responsible for mannose-sensitive haemagglutination is abolished. The cloned V. cholerae peptidase processes either EpsI or MshA preproteins when co-expressed in E. coli. Mutation of the V. cholerae peptidase gene also results in a defect in virulence and decreased levels of OmpU. The V. cholerae peptidase gene sequence shows 80% homology with the Vibrio vulnificus VvpD type 4 prepilin peptidase required for pilus assembly and cytolysin secretion in V. vulnificus. Accordingly, the V. cholerae type 4 prepilin peptidase required for pilus assembly and cholera toxin secretion has been designated VcpD.

Para Bombay phenotype--a case report

Bombay phenotype is peculiar in that red cells are not agglutinated by antisera A, B or H; while serum contains anti A, B and H. Existence of modifying genes at independent loci with variable expression of ABO genes is postulated. We report here a case of partial suppression where antigens could be detected by elution tests and unlike classical Bombay type, normal amount of appropriate blood group substances were present in saliva. This case of para Bombay phenotype was detected as a result of discrepancy in cell and serum group ng. This highlights the importance of both forward and reverse grouping in ABO testing.

Transcriptional regulation of the Yersinia pseudotuberculosis pH6 antigen adhesin by two envelope-associated components

The Yersinia pseudotuberculosis pH6 antigen mediates haemagglutination and adhesion to cultured mammalian cells. The synthesis of pH6 antigen requires the products of the psaEFABC genes in both Yersinia pseudotuberculosis and Escherichia coli. In-frame deletion mutations of psaE and psaF caused defective haemagglutination. In contrast, we showed that the psaABC genes were sufficient for haemagglutination if they were expressed by a heterologous promoter. Environmental regulation of pH6 antigen by temperature and pH occurs via regulation of the major pilus protein PsaA at the transcriptional level. Northern blot analyses indicate that the psaA transcript was absent in either psaE or psaF mutant strains. Primer extension analyses indicate that, in Y. pseudotuberculosis, the transcription of the psaE and psaF genes is constitutive. Alkaline phosphatase fusion studies confirm the topology prediction that PsaE and PsaF are both inner-membrane-associated proteins. PsaE consists of an N-terminal cytoplasmic domain, containing sequence similarity to transcriptional regulators found in two-component systems as well as to the Salmonella typhimurium HIIA protein, with a C-terminal domain that is periplasmically localized. PsaF is predicted to be oriented with most of the protein in the periplasm, the hydrophobic N-terminus being either integrated in the inner membrane or cleaved as a signal peptide.

The psa locus is responsible for thermoinducible binding of Yersinia pseudotuberculosis to cultured cells

Yersinia pseudotuberculosis inv mutant strains cured of the virulence plasmid exhibit thermoinducible adhesion to cultured mammalian cells. To identify the genes responsible for this phenotype, Y. pseudotuberculosis homologs of the Y. enterocolitica ail and the Y. pestis psa loci were identified. Mutations in the Y. pseudotuberculosis ail and psa loci were constructed and tested for thermoinducible binding. Results of cellular binding assays indicated that only mutations in psa, not in ail, resulted in defects for thermoinducible binding, with inv yadA psa strains showing no detectable cell adhesion. In addition, an inv psa strain was defective for hemagglutination of sheep erythrocytes, in contrast to an inv psa+ strain which was fully competent for hemagglutination. The introduction of a plasmid containing a 6.7-kb KpnI-ClaI fragment of Y. pseudotuberculosis encompassing the psa locus was sufficient to complement both the cell adhesion and hemagglutination defects of the psa mutant. Results from subcloning and transposon mutagenesis indicated that the complete 6.7-kb region was required for thermoinducible binding and hemagglutination.

Genetic evidence for the relationship of Porphyromonas gingivalis cysteine protease and hemagglutinin activities

Cysteine protease and hemagglutinin activities of Porphyromonas gingivalis have been implicated as virulence factors in periodontitis. In addition, a close structural relationship between these factors has been suggested. In order to examine the molecular basis for such a relationship, we constructed an isogenic mutant, G-102, of P. gingivalis 381 deficient in Arg-gingipain cysteine protease activity. The mutant displayed not only reduced protease activity but also significantly reduced hemagglutination activity compared with the wild-type strain. Therefore, this investigation provided genetic evidence for the recently proposed structural relationship between Arg-gingipain and the hemagglutinin activity of P. gingivalis strains.

Molecular analysis of the cso operon of enterotoxigenic Escherichia coli reveals that CsoA is the adhesin of CS1 fimbriae and that the accessory genes are interchangeable with those of the cfa operon

A deletion mutation in csoA, the gene encoding the structural subunit protein of CS1 fimbriae of enterotoxigenic Escherichia coli of serotype O6:K15:H16 or H-, was constructed in the subcloned CS1 genetic determinant. The mutation resulted in the abolition of CS1 fimbrial adhesiveness. Complementation, in trans, involving the determinant with the csoA deletion mutation and the gene encoding the structural subunit protein, CsoA, expressed from compatible plasmids, restored the expression and adhesive ability of CS1 fimbriae. In addition, trans-complementation was achieved between the cso determinant with the aforementioned deletion mutation and the cfaB gene encoding the structural subunit protein (CfaB) of CFA/I fimbriae, resulting in the expression of CFA/I fimbriae. The observation that heterologous assembly was possible between these two fimbrial systems, together with the knowledge that the adhesin of CFA/I fimbriae is the structural subunit, was exploited to investigate whether CsoA had adhering properties. A deletion mutation in cfaB was created in the CFA/I fimbrial determinant. Complementation of this mutation with csoA in trans resulted in expression of the CsoA antigen on the bacterial cell surface and restoration of bacterial adherence. As no minor subunits act as the adhesin in CFA/I fimbriae, adhesion was mediated by CsoA. Nucleotide sequencing of the DNA region downstream from csoA confirmed the absence of genes encoding minor subunits which might act as the adhesin. Two open reading frames were revealed which encoded proteins sharing considerable homology with proteins encoded by corresponding ORFs in the CFA/I fimbrial operon. These proteins underlie the functional similarities between the CS1 and CFA/I fimbrial systems, allowing heterologous expression of their respective subunits.

Mapping the hemagglutination domain of rotaviruses

Most strains of animal rotaviruses are able to agglutinate erythrocytes, and the surface protein VP4 is the virus hemagglutinin. To map the hemagglutination domain on VP4 while preserving the conformation of the protein, we constructed full-length chimeras between the VP4 genes of hemagglutinating (YM) and nonhemagglutinating (KU) rotavirus strains. The parental and chimeric genes were expressed in insect cells, and the recombinant VP4 proteins were evaluated for their capacity to agglutinate human type O erythrocytes. Three chimeric genes, encoding amino acids 1 to 208 (QKU), 93 to 208 (QC), and 93 to 776 (QYM) of the YM VP4 protein in a KU VP4 background, were constructed. YM VP4 and chimeras QKU and QC were shown to specifically hemagglutinate, indicating that the region between amino acids 93 and 208 of YM VP4 is sufficient to determine the hemagglutination activity of the protein.

Genetic analysis of echovirus 11 variability in adsorption to human erythrocytes

The frequency of nonhemagglutinating (h-) mutants was determined in hemagglutinating (HA) clones of echovirus 11. The HA clones were derived from the prototype strain Gregory and a clinical isolate of echovirus 11. The h- mutants were found at a constant frequency of 3.0 x 10(-5) (mean value) in the HA clones derived from both strains. Since the conditions of the population equilibrium of HA clones and neutrality of the mutation were satisfied, it was proposed that the observed frequency of h- mutants occurred as a result of a point mutation. The frequency of h+ revertants at the second passage of h- mutant clone was 9.1 x 10(-5). Hence the frequency of reversion suggests that the number of potential sites of back mutation was restricted.

Correlation of haemagglutination activity with trypsin-like protease activity of Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium associated with various forms of periodontal disease. Several characteristics of P. gingivalis are thought to contribute to its pathogenicity; these include haemagglutination and trypsin-like protease activity. Previous studies suggest an association between haemagglutination and trypsin-like protease activity of P. gingivalis. To investigate this, two complementary quantitative experimental approaches were taken. Five independent mutants of P. gingivalis deficient in trypsin-like protease activity were shown to exhibit reduced haemagglutination activity. In addition, enhancers (cysteine and dithiothreitol) and inhibitors (N-ethylmaleimide, N-p-tosyl-L-lysine-chloromethyl ketone, and phenylmethylsulphonyl fluoride) of trypsin-like protease activity were shown, respectively, to significantly enhance and inhibit haemagglutination activity of washed, wild-type P. gingivalis cells (p less than 0.05, paired t-test). Statistical analysis indicated a strong correlation between haemagglutination and trypsin-like protease activity (r = 0.85, p less than 0.001, Spearman rank correlation). The effect of the protease enhancers and inhibitors on haemagglutination activity was specific for P. gingivalis, as they did not significantly change the haemagglutination activity of Fusobacterium nucleatum. These results suggest that the proteolytic site of the trypsin-like protease participates in haemagglutination activity of P. gingivalis.

Potential role of phase variation of type 1 pili in urinary tract infection. and bacterial prostatitis

Adherence of Escherichia coli to uroepithelial cells is an important step in the pathogenesis of urinary tract infection. The process is frequently mediated by pili which undergo phase variation in response to changes in environmental growth conditions in vitro. It is possible that phase variation of pili and other bacterial virulence factors may play a role in the pathogenesis of bacterial prostatitis. The obvious differences in the environmental conditions of urethra, bladder, and prostate could favor strains that have the ability to adapt. For example, adhesion to the urethral and bladder mucosa could be facilitated by pili and their expression could be advantageous in the early phase of prostatitis. However, after the prostate ducts are colonized, pili may be detrimental since they can render E. coli more susceptible to phagocytosis. Further studies on phase variation of virulence factors of bacteria that cause prostatitis appear warranted.