Use of TrpE/Gag fusion proteins to characterize immunoreactive domains on the human immunodeficiency virus type 1 core protein

Recognition of ovine lentivirus gag gene products by serum from infected sheep

In order to localize the immunodominant regions, 12 ovine lentivirus (OLV) gag-coding gene fragments were cloned and expressed in Escherichia coli and then tested in a Western blot (WB) assay against a panel of sera collected from US and Italian OLV-infected sheep. The most immunoreactive regions were mapped to the amino-terminal of p25 and carboxyl-terminal of p14. In addition, we found that the reactivity pattern between US and Italian sheep was very similar, suggesting the antigenic domain between US and Italian isolates in the gag gene structures could be conserved. Given the broad immunoreactivity of the amino-terminal of p25, this region could serve as an ideal diagnostic antigen for the serological identification of OLV-infected sheep.

Identification and mapping of the gene encoding the glycoprotein complex gp82-gp105 of human herpesvirus 6 and mapping of the neutralizing epitope recognized by monoclonal antibodies

Monoclonal antibodies (MAbs) 2D4, 2D6, and 13D6 against human herpesvirus 6 (HHV-6) variant A strain GS recognized virion envelope glycoprotein complex gp82-gp105 and neutralized the infectivity of HHV-6 variant A group isolates. A 624-bp genomic fragment (82G) was identified from an HHV-6 strain GS genomic library constructed in the lambda gt11 expression system by immunoscreening with MAb 2D6. Rabbit antibodies against the fusion protein expressed from the genomic insert recognized glycoprotein complex gp82-gp105 from HHV-6-infected cells, thus confirming that the genomic fragment is a portion of the gene(s) that encodes gp82-gp105. This genomic insert hybridized specifically with viral DNAs from HHV-6 variant A strains GS and U1101 under high-stringency conditions but hybridized with HHV-6 variant B strain Z-29 DNA only under low-stringency conditions. DNA sequence analysis of the insert revealed a 167-amino-acid single open reading frame with an open 5' end and a stop codon at the 3' end. Hybridization studies with HHV-6A strain U1102 DNA localized the gp82-gp105-encoding gene to the unique long region near the direct repeat at the right end of the genome. To locate the neutralizing epitope(s) recognized by the MAbs, a series of deletions from the 3' end of the gene were constructed with exonuclease III, and fusion proteins from deletion constructs were tested for reactivity with MAbs in a Western immunoblot assay. Sequencing of deletion constructs at the reactive-nonreactive transition point localized the epitope recognized by the three neutralizing MAbs within or near a repeat amino acid sequence (NIYFNIY) of the putative protein. This repeat sequence region is surrounded on either side by two potential N-glycosylation sites and three cysteine residues.

Mapping of linear B-cell epitopes on the major core protein p24 of human immunodeficiency virus type 1 (HIV-1)

Three murine monoclonal antibodies (MAbs) F5-2, F5-4, and F5-16 defining three different epitopes on the major core protein p24 of the human immunodeficiency virus type 1 (HIV-1) were epitope mapped using a random fragment expression library representing the p17- and p24-encoding part of the gag open reading frame. F5-2 defined an epitope within amino acids (aa) 14-23 at the N-terminus of p24, and F5-4 defined an epitope within aa 153-174 in the C-terminus of p24. F5-16 did not recognize any of the fusion proteins produced by the expression library indicating that this MAb defines a true conformational epitope on p24. Since the N-terminus of p24 has been reported to be immunosilent in humans, 356 HIV-1 antibody-positive serum samples were tested for reactivity against the region of p24 defined by F5-2. More than one third of the samples recognized this region indicating that it is immunoreactive and, further, the presence of antibodies against this region was associated with a reduced CD4 cell count.

Fine molecular specificity of linear and assembled antibody binding sites in HIV-1 p24

A set of seven murine monoclonal antibodies were generated against a chemically synthesized 11-kDa 104-mer peptide covering the C-terminal residues 270-373 of the p24 gag protein (HIV-1BRU strain). All monoclonal antibodies recognized HIV-1IIIB infected MOLT3 cells by fluorescence and gave positive Western blot signals with viral gag peptides (p55 and/or p24). Oligopeptide binding regions were located with competitive enzyme-linked immunosorbent assays. Detailed epitope scanning analyses (the Geysen technique) were performed by serological testing of the monoclonal antibodies against 99 overlapping hexapeptides which corresponded to the entire 104-mer region. The antibodies bound to p24 peptide sequences located within the 275-293 and 351-368 regions. One antibody (LH104-B) which reacted with residues 357-362 bound to p55 alone. In contrast, another antibody (LH104-I), which recognized the residues 358-363, i.e. with five out of six residues in common with antibody LH104-B for its epitope region, reacted exclusively with p24. At least two of the antibodies (LH104-C and -A) which bound to p24 alone, apparently recognized conformational epitopes. They gave positive reactions with the regions 288-293/351-356 and 284-289/351-356, respectively. This work shows that chemical synthesis of large peptides is a viable alternative approach to immunochemical studies of viral proteins.

Expression of functional beta-galactosidase containing the coxsackievirus 3C protease as an internal fusion

Alpha complementation of beta-galactosidase (beta gal) is intracistronic and requires interaction between the alpha donor region (residues 3-41) and alpha acceptor fragment (produced by M15). We have constructed two plasmids which direct the synthesis of hybrid beta gal: coxsackievirus proteins in Escherichia coli. One plasmid, pBD1045, encodes an enzymatically active 3C protease of coxsackievirus B3 fused between the amino-terminal 79 amino acids of beta gal (containing the alpha donor region) and amino acids 80 to 1023 (alpha acceptor region). A second plasmid, pBD1043 encodes an inactive 3C protease and results in a fusion of 260 coxsackievirus amino acids between residues 79 and 80 of the beta gal monomer. Both hybrid proteins expressed by these constructs have beta-galactosidase activity regardless of whether the viral protease (183 amino acids) is autocatalytically cleaved out of the chimeric protein (pBD1045) or remains as part of a fusion protein (pBD1043). The implications of these results for structural flexibility of the complemented beta-galactosidase enzyme are discussed.

Characterization of the antigenic domains of the major core protein (p26) of equine infectious anemia virus

A panel of recombinant trpLE-gag fusion proteins and synthetic peptides was used in Western immunoblot and enzyme-linked immunosorbent assays to identify segments of the major core protein (p26) of equine infectious anemia virus that are antigenic in horses during experimental and natural infections with the virus. The predominant humoral immune response was directed toward a highly immunogenic domain composed of 83 amino acids from the carboxy terminus of p26. The observed immunogenicity of p26 resembled that reported for p24 of human immunodeficiency virus type 1, suggesting the conservation of structural motifs in the lentiviral core proteins which are responsible for their observed immunogenicity during persistent lentivirus infections.

Peptide component vaccine engineering: targeting the AIDS virus

Most of the successful vaccines developed to date induce protective immunity resembling that produced by natural infection. HIV infection does not induce protective immunity. Thus, previously successful approaches based on live- or killed-virus preparations may not yield an effective and safe AIDS vaccine and many feel that a more highly engineered vaccine will be required. Synthetic peptides represent extremely powerful tools for vaccine research and construct optimization. The theory and practice of vaccine engineering using synthetic peptide components is reviewed with special emphasis on progress towards development of a vaccine for AIDS.

Mapping of viral epitopes with prokaryotic expression products

Several systems are available for the expression of foreign gene sequences in Escherichia coli. We describe the use of prokaryotic expression products of viral gene fragments in order to identify the regions that specify the binding sites of antibodies. This approach is particularly successful if the antigenicity does not depend on the native protein, but only on the amino acid sequence, i.e., if the epitope is sequential. Combining prokaryotic expression with the use of synthetic peptides often permits a fast and accurate mapping of an epitope. The occurrence of immunodominant sequential epitopes on the surfaces of viruses seems to be a widespread phenomenon.