Development of peptide mimics of a protective epitope of Vibrio cholerae Ogawa O-antigen and investigation of the structural basis of peptide mimicry.
As an alternative approach toward the development of a cholera vaccine, the potential of peptide mimics of Vibrio cholerae lipopolysaccharide (LPS) to elicit cross-reactive immune responses against LPS was investigated. Two closely related protective monoclonal antibodies, S-20-4 and A-20-6, which are specific for Ogawa O-antigen (O-specific polysaccharide; O-SP) of V. cholerae O1, were used as the target antibodies (Abs) to pan phage display libraries under different elution conditions. Six phage clones identified from S-20-4 panning showed significant binding to both S-20-4 and A-20-6. Thus, it is likely that these phage-displayed peptides mimic an important conformational epitope of Ogawa antigens and are not simply functionally recognized by S-20-4. Each of the six phage clones that could bind to both monoclonal antibodies also competed with LPS for binding to S-20-4, suggesting that the peptides bind close to the paratope of the Ab. In order to predict how these peptide mimics interact with S-20-4 compared with its carbohydrate counterpart, one peptide mimic, 4P-8, which is one of the highest affinity binders and shares motifs with several other peptide mimics, was selected for further studies using computer modeling methods and site-directed mutagenesis. These studies suggest that 4P-8 is recognized as a hairpin structure that mimics some O-SP interactions with S-20-4 and also makes unique ligand interactions with S-20-4. In addition, 4P-8-KLH was able to elicit anti-LPS Abs in mice, but the immune response was not vibriocidal or protective. However, boosting with 4P-8-KLH after immunizing with LPS prolonged the LPS-reactive IgG and IgM Ab responses as well as vibriocidal titers and provided a much greater degree of protection than priming with LPS alone.
Dharmasena
Madushini N
MN
Department of Microbiology and Immunology, Dartmouth Medical School, Hanover, New Hampshire, 03755.
Jewell
David A
DA
Department of Genetics, Dartmouth Medical School, Hanover, New Hampshire 03755.
Taylor
Ronald K
RK
Department of Microbiology and Immunology, Dartmouth Medical School, Hanover, New Hampshire, 03755. Electronic address: Ronald.K.Taylor@dartmouth.edu.
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D001667:Binding, Competitive; D000939:Epitopes / Q000737:chemistry*; D005260:Female; D006863:Hydrogen-Ion Concentration; D008070:Lipopolysaccharides / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019081:O Antigens / Q000737:chemistry; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry*; D014734:Vibrio cholerae / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D000939:Epitopes; D008070:Lipopolysaccharides; D019081:O Antigens; D019151:Peptide Library; D010455:Peptides