IDENTIFICATION OF SURFACE-EXPOSED LINEAR B-CELL EPITOPES OF THE NONFIMBRIAL ADHESIN CS31A OF ESCHERICHIA-COLI BY USING OVERLAPPING PEPTIDESAND ANTIPEPTIDE ANTIBODIES
Mc. Mechin et al., IDENTIFICATION OF SURFACE-EXPOSED LINEAR B-CELL EPITOPES OF THE NONFIMBRIAL ADHESIN CS31A OF ESCHERICHIA-COLI BY USING OVERLAPPING PEPTIDESAND ANTIPEPTIDE ANTIBODIES, Infection and immunity, 64(9), 1996, pp. 3555-3564
As a first step toward the design of an epitope vaccine, by using the
nonfimbrial adhesin CS31A of Escherichia coli as a carrier, a low-reso
lution topological and epitope map of the CS31A subunit was developed
by using solid-phase peptide synthesis and polyclonal rabbit antibodie
s raised against both native and denatured proteins. Peptides constitu
ting antigenic epitopes on the major subunit (ClpG) of the multimeric
CS31A antigen were identified by examining the binding of the antibodi
es to 249 overlapping nonapeptides covering the amino acid sequence of
ClpG, With antibodies raised against denatured ClpG subunit, seven ma
jor epitope regions, corresponding to residues 10 to 18, 45 to 58, 88
to 107, 148 to 172, 187 to 196, 212 to 219, and 235 to 241, were locat
ed. Most of the epitopes were hydrophilic and were located in variable
regions, residing largely in loop regions at the boundaries of second
ary structural elements of ClpG, In contrast, antibodies raised agains
t native CS31A antigen reacted only with the peptide AVNPNA (positions
179 to 184), demonstrating that this peptide was the only linear B-ce
ll epitope of the native protein, The different immunogenic profiles o
f native CS31A antigen and denatured ClpG indicated that the denaturat
ion process resulted in marked conformational changes in the protein,
which could expose epitopes hidden or absent in native CS31A. To ident
ify the surface-exposed epitopes, nine peptides covering the dominant
antigenic regions of ClpG were synthesized and used to prepare site-sp
ecific antibodies. Antipeptide antibodies were tested, in a competitiv
e enzyme-linked immunosorbent assay (ELISA), for cross-reactivity with
native CS31A and denatured ClpG subunit, Four of these antipeptide an
tibodies bound to the native protein in an accessibility ELISA, indica
ting that residues 44 to 56, 174 to 190, 185 to 199, and 235 to 249 we
re surface exposed on CS31A. These data indicate that an immunodominan
t surface-exposed linear epitope was present in the region from positi
ons 179 to 184 of ClpG in the native CS31A antigen on intact bacterial
cells and suggest that the four surface-exposed epitopes constitute p
otential sites for insertions or substitutions with heterologous pepti
des.