Development and Use of Receptor Binding Peptides Derived From Antireceptor Antibodies

Bacterial expression and characterization of recombinant biologically active anti-tyrosine kinase receptor antibody forms

Homomeric and heteromeric interactions among cell-surface tyrosine kinase receptors belonging to the ErbB family lead to intracellular signaling cascades which are involved in cell activation, cytoskeletal interactions, and cellular transformation leading to neoplasia. Monoclonal antibodies which specifically bind to p185neu or epidermal growth factor receptor (EGFR), such as 7.16.4 and 225, respectively, can elicit tumor growth-inhibitory effects on transformed cells which overexpress either or both of these receptors. In order to better understand these receptor-receptor and receptor-antibody interactions and to gain insights that may be useful in the production and design of an antibody-based anticancer therapeutic, novel small recombinant 7.16.4 and 225 single-chain Fv fragments (scFv) were constructed, expressed, and characterized. We showed that these recombinant antibody fragments, which retain binding affinity, can be produced and purified from bacterial cell lysates. Our analyses further demonstrate that fusion of a 61 amino-acid dimerization domain with 7.16.4 and 225 scFv (7.16.4hth and 225hth) is sufficient to restore biological activity to these recombinant proteins.

Molecular characterization of a human anti-HIV 1 monoclonal antibody revealed a CD26-related motif in CDR2

Genes encoding the immunoglobulin variable regions of a human anti-HIV-1 IgG1 kappa monoclonal antibody were rescued from a hybridoma, derived from a sero-negative donor, using PCR cloning and expression in Escherichia coli. The ELISA binding results obtained from the expressed Fab fragment confirmed the anti-V3 loop specificity for HIV-1 (LAI) of the original antibody. In addition, an amino acid sequence derived from the second complementarity determining region (CDRH2) of the heavy chain was found to be very similar to the catalytic motif of CD26, a T-cell activation antigen. Furthermore, synthetic peptides containing both the catalytic domain of CD26 and CDRH2 of the antibody showed specific binding to an HIV peptide representing the V3 region in a dose-dependent manner. This suggests an involvement of CD26 as a possible coreceptor for HIV-1.

Interaction of lysozyme with synthetic anti-lysozyme D1.3 antibody fragments studied by affinity chromatography and surface plasmon resonance

Synthetic antibody fragments of monoclonal anti-lysozyme antibody D1.3 have been tested on binding with hen egg white lysozyme using immunoaffinity chromatography and surface plasmon resonance. Upon immunoaffinity chromatography, peptides containing one or two complementarity determining regions (CDRs) of D1.3 show interaction with lysozyme. Surface plasmon resonance with immobilized CDR peptides showed that this interaction is not based on the antigen-antibody interaction. Nevertheless, these peptides could be useful as ligands for the purification of lysozyme from a mixture of proteins.

Anti-idiotypic antibodies against the kinin receptor

Three sets of monoclonal antibodies against bradykinin (MBK1, MBK2, MBK3) were generated by somatic cell fusion, characterized by their peptide specificity and compared to the known ligand specificity of the kinin receptor subtypes. By these criteria the paratope of MBK3 resembled the B2 receptor binding site whereas MBK1 shared principal binding characteristics with the B1 recrptor. Anti-idiotypic antibodies against MBK1, MBK2 and MBK3 were raised in rabbit and sheep. Specificity of the network components was verified by inhibition experiments on the level of peptide, idiotype and anti-idiotype. Anti-idiotypic antibodies against MBK3 recognized a conformation-dependent epitope which was binding site-related. Binding studies on human foreskin fibroblasts and guinea pig ileum showed mutual displacement of the anti-idiotypic antibody and bradykinin at the binding site pointing to a specific interaction of the antibody with the receptor from various species. An agonist activity of the antibodies, demonstrated in human (inositolphosphate pathway) and mouse (prostaglandin pathway) fibroblasts indicated that the anti-idiotypes bear an internal image of the ligand epitope. This molecular mimicry which was further substantiated by the detection of bradykinin specific anti-idiotypic antibodies, provides the structural basis for the observed cross-reactivity over species borders.

Synthetic antibody fragment as ligand in immunoaffinity chromatography

The possibility that a fragment of an antibody molecule may interact with a protein antigen was tested by studying the binding properties of a thirteen-residue synthetic peptide with an amino acid sequence similar to part of a hypervariable segment of a monoclonal antibody directed against lysozyme. Affinity adsorbents were prepared with this peptide and with non-related peptides as ligand. Non-specific interactions could be abolished by washing the column with 0.05 M sodium thiocyanate in 20 mM tris-HCl (pH 7.4). Lysozyme was only bound to the antilysozyme adsorbent and could be eluted with 1 M sodium thiocyanate. The results show that immunoaffinity chromatography with synthetic peptide ligands which mimic the antigen-binding site may be a useful tool in the selective purification of proteins.