Purification and characterization of novel hemagglutinins from Vibrio mimicus: a 39-kilodalton major outer membrane protein and lipopolysaccharide

Adherence, anti-adherence, and oligosaccharides preventing pathogens from sticking to the host

For many pathogenic bacteria, infections are initiated only after the organism has first adhered to the host cell surface. If adherence can be inhibited, then the subsequent infection can also be inhibited. This approach forms the basis of anti-adherence strategies, which have been devised to prevent a variety of bacterial infections. In this chapter, the molecular basis by which respiratory, urinary, and gastrointestinal tract pathogens adhere to host cells will be described. The five general types of anti-adherence agents will also be reviewed. The most well-studied are the receptor analogs, which include oligosaccharides produced synthetically or derived from natural sources, including milk, berries, and other plants. Their ability to inhibit pathogen adherence may lead to development of novel, food-grade anti-infective agents that are inexpensive and safe.

Proteolytic activation of Vibrio mimicus (Vm) major outer membrane protein haemagglutinin (HA) with Vm-HA/protease: Implication for understanding bacterial adherence

Vibrio mimicus (Vm) haemagglutinins (HAs), such as an extracellular HA/protease (Vm-HA/protease) and a major outer membrane protein-HA (Vm-OMPHA), have been recognized as the putative adherence factors for the bacterium. However, the mechanism by which HAs coordinate the adherence function of the bacterium remains as yet unknown. We report herein the positive interaction between Vm-HA/protease and Vm-OMPHA resulting in significant enhancement of the haemagglutinating ability. In this interaction, no cleaved polypeptide was detected; however, limited proteolysis of Vm-OMPHA was confirmed by SDS-PAGE. The proteolytic activation of the native cell-associated Vm-OMPHA by limited proteolysis was also demonstrated in several V. mimicus strains. Proteolytic activation of OMPHA was also achieved with various proteases from bacterial and eukaryotic sources. These findings may indicate a novel coordination of V. mimicus HAs in the adherence of the bacterium.

The FAXWXXT motif in the carboxyl terminus ofVibrio mimicusmetalloprotease is involved in binding to collagen

We have shown previously that the C-terminal region of the extracellular metalloprotease of Vibrio mimicus (VMC) is essential for collagenase activity. Here, we demonstrate that deletion of 100 amino acids, but not 67 amino acids, from the C-terminus of the intact VMC protein (VMC61) abolished the collagenase activity. The intervening 33-amino acid region contains a repeated FAXWXXT motif that is essential for insoluble type I collagen binding; the isolated 33-amino acid peptide bound to insoluble type I collagen, while a peptide containing only the first FAXWXXT motif did not. Compared to the VMC61, the 33-amino acid peptide corresponding to the C-terminus exhibited a similar binding affinity and a lower binding capacity.

Identification of a 19.3-kDa protein in MRHA-positive Edwardsiella tarda: putative fimbrial major subunit

The hemagglutinating properties of Edwardsiella tarda isolated from fish were investigated. Hemagglutination of E. tarda was not inhibited by D-mannose but was strongly inhibited by fetuin and N-acetylneuraminic acid. Extraction of hemagglutinating activity from bacterial cells was achieved using n-octyl-beta-D-thioglucoside (NOTG), and the NOTG extracts were fractionated by sucrose density gradient ultracentrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the fractions revealed that a 19.3-kDa protein band appeared in the fractions exhibiting highest hemagglutinating activity. In an immunoblot analysis of NOTG extracts from 18 strains of E. tarda, the 19.3-kDa protein was detected only in the extracts possessing hemagglutinating activity. The predicted amino acid sequence of a 534-bp gene encoding the 19.3-kDa protein was identical to fimbrial subunit (FimA) of E. tarda by FASTA homology search. These findings suggest that fimbriae are implicated in the hemagglutination of E. tarda.

Characterization of the enzyme activity of an extracellular metalloprotease (VMC) from Vibrio mimicus and its C-terminal deletions

To investigate the enzymatic properties of Vibrio mimicus metalloprotease, the mature metalloprotease gene (vmc) was overexpressed in Escherichia coli and the recombinant protein (rVMC61) was purified by metal affinity chromatography. rVMC61 showed maximum activity at about 37 degrees C, pH 8. The purified rVMC61 was very specific toward collagen substrates, such as gelatin, type I, II, and III collagens and synthetic peptides (Cbz-GPLGP and Cbz-GPGGPA). But it did not show degrading activity toward other biological proteins including lysozyme, lactoferrin and bovine serum albumin. rVMC61 also showed cytotoxicity against CHSE-214 fish cells. To examine the role of the C-terminal region of rVMC61, the 3' end of the metalloprotease gene (vmc) was digested serially with exonuclease III. The truncated vmc derivatives encoding 57-42 kDa of the protease were isolated and overexpressed in E. coli. The collagenase activities of truncated proteins were investigated using gelatin as substrate. Deletion of 100 amino acids from the C-terminus resulted in loss of gelatin degrading activity. However, deletion of 67 amino acids from the C-terminus did not affect its gelatin degrading activity.

Vibrio mimicus attaches to the intestinal mucosa by outer membrane hemagglutinins specific to polypeptide moieties of glycoproteins

Vibrio mimicus is the closest organism to Vibrio cholerae. V. mimicus E-33, which is a highly adhesive and enteropathogenic strain, is known to produce three types of hemagglutinins (HAs), i.e., a 31-kDa exocellular metalloprotease (Vm-HA/protease), lipopolysaccharide (Vm-LPSHA), and a 39-kDa major outer membrane protein (Vm-OMPHA). Hemagglutination induced by Vm-LPSHA and Vm-OMPHA was inhibited by glycoproteins, including mucin, fetuin, and asialofetuin, but not by monosaccharides, disaccharides, or N-acetylated saccharides. The inhibitory potential of each glycoprotein for Vm-OMPHA was greatly augmented by treatment with a glycolytic enzyme such as beta-D-galactosidase or beta-D-glucosidase, while pronase treatment achieved complete abolition of the inhibitory potential. The inhibitory ability of the glycoproteins for Vm-LPSHA was also abolished by pronase treatment; however, glycolytic enzyme treatment showed no effect. Hence, the polypeptide portion of glycoproteins may directly associate with Vm-OMPHA and Vm-LPSHA, but the sugar moiety may act as a barrier to interaction with Vm-OMPHA. The glycoproteins as well as Fab antibodies against Vm-OMPHA and Vm-LPSHA eliminated the ability of E-33 cells to agglutinate rabbit erythrocytes and to attach to rabbit intestinal mucosa. Additionally, expression of the hemagglutinating ability by the bacterial cells was accompanied by efficient bacterial adherence to the intestinal mucosa. Finally, the hemagglutinating activity of Vm-OMPHA was markedly increased by incubation with Vm-HA/protease. These results indicate that all three HAs may have significant roles in the glycoprotein-mediated intestinal adherence of V. mimicus E-33.

Hemagglutination is a novel biological function of lipopolysaccharide (LPS), as seen with the Vibrio cholerae O139 LPS

It has been generally thought that the polysaccharide moiety of lipopolysaccharide (LPS) maintains only serological specificity, while the lipid A portion determines various biological functions. However, we found that hemagglutination was a common function of the polysaccharide moiety of LPSs from important human enteropathogenic bacteria. Of the LPSs examined, Vibrio cholerae O139 LPS showed the highest hemagglutinating activity. Glycoproteins, such as mucin and fetuin, showed efficient inhibition of the hemagglutinating ability. Since cell-mediated hemagglutination is known to be correlated with bacterial adherence, hemagglutination induced by the polysaccharide moiety is interpreted to indicate that cell-surface LPS is a potential adhesin.

Pathogenic vibrios in the natural aquatic environment

In recent years, members belonging to the genus Vibrio of the family Vibrionaceae have acquired increasing importance because of the association of several of its members with human disease. The most feared of the Vibrio species is Vibrio cholerae, the causative agent of cholera, a devastating disease of global significance. Other important vibrios of medical importance are V. parahemolyticus, V. vulnificus, V. mimicus, and to a lesser extent V. fluvialis, V. furnissii, V. hollisae, and V. damsela. Recent studies have also implicated V. alginolyticus and V. metschnikovii in human disease, although their complete significance has not yet been established. The virulence of all medically important vibrios is aided by a variety of traits that help breach human defenses. In this review, we provide an overview of the environmental distribution of the pathogenic vibrios and the important virulence traits that enable them to cause disease.