Effects of amino acid substitutions outside an antigenic site on protein binding to monoclonal antibodies of predetermined specificity obtained by peptide immunization: demonstration with region 15-22 (antigenic site 1) of myoglobin

Epitopic analysis and quantification of bovine myoglobin with monoclonal antibodies

Seven rat monoclonal antibodies (MAb) for bovine myoglobin were produced. Five antibodies reacted with surface-absorbed myoglobin whereas the two remainders reacted only in a sandwich type ELISA. The ability of different antibodies to bind simultaneously to myoglobin was examined by competition and additivity experiments and three noncompeting epitope regions were found. A two-site enzyme immunoassay was developed and allowed quantification of 30 ng/ml bovine myoglobin. These antibodies should be valuable tools in comparative studies for immunological reactivity of mammalian myoglobins and for myoglobin measurement in serum and urine of myopathic animals.

Role of hydrophobic and hydrophilic forces in peptide-protein interaction: new advances

A considerable part of important biological processes is governed by the noncovalent association of peptides and proteins. Various types of intermolecular forces may be involved in the formation of these molecular assemblies. This review gives a brief account of the physicochemical bases of interactive forces, with special emphasis on their impact on various peptide-protein interactions; summarizes the newest biochemical and biophysical methods for the study of such interactions; and discusses the role of various hydrophilic and hydrophobic forces in peptide-protein interactions in various fields of life sciences, such as immunology, enzymology, receptor binding, and toxicology.

Improbability of harmful autoimmune responses resulting from immunization with HIV-1 envelope glycoproteins

Autoimmunity mediated by cross-reactive antibodies, elicited by HIV-1 envelope glycoproteins gp120/gp160, has been postulated to contribute to the pathogenesis of AIDS. Partial amino acid sequence homology between gp120/gp160 and several human host proteins, including MHC antigens and immunoglobulins, has been perceived as the basis for immunological cross-reactivity. Binding of antibodies from sera of HIV-1-infected individuals to selected host proteins and/or to synthetic peptides derived from them and the inhibitory activity of such sera in assays measuring the functional activity of T cells provided apparent support for the autoimmunity hypothesis, which is also relevant to the issue of safety of anti-HIV-1 vaccines. Considering the possibility that the detected autoantibodies may arise for reasons other than antibody responses to gp120/gp160, the immunological cross-reactivity between gp120/gp160 and the relevant host proteins was investigated using hyperimmune rabbit anti-gp120/gp160 and monoclonal antibodies. As determined from dilution end-point comparisons for polyclonal anti-gp120, the cross-reactivity of anti-gp120 with CD4 was undetectable (< 10(-5)%). The cross-reactivity of anti-gp120/gp160 with HLA-I and HLA-II antigens was also undetectable (< 4 x 10(-4)%) and that with other human proteins reported to have partial sequence homology with gp120/gp41 was < or = 0.013%. Anti-gp120/gp160 did not have detectable inhibitory effects in functional assays measuring proliferative T cell responses. Therefore, immunization with gp120/gp160 is unlikely to elicit harmful autoimmune responses.

Effects of amino acid substitutions outside an antigenic site on protein binding to monoclonal antibodies of predetermined specificity obtained by peptide immunization: demonstration with region 113-120 (antigenic site 4) of myoglobin

Immunochemical cross-reactivity of protein variants has been very frequently used to map protein antigenic sites. The approach is based on the assumption that amino acid substitutions affecting the binding of a protein to its antibody, particularly when monoclonal antibodies (mAbs) are used, must be part of the antigenic site and not far from it. The assumption was investigated in this study by determining the effects of amino acid substitutions outside the antigenic site on the reactivity of six myoglobin (Mb) variants with three mAbs of predetermined specificity prepared by immunization with a free synthetic peptide representing region 113-120 (antigenic site 4) of Mb. Two of the Mb variants used had no substitutions within residues 113-120 (the region to which the specificity of the mAbs is directed) and yet exhibited markedly decreased cross-reactions and binding affinities, relative to the reference antigen, sperm-whale Mb. The other three Mb variants possessed substitutions within, as well as outside, region 113-120 and showed very little cross-reactivities. The results of this study, particularly with the Mbs that have no substitutions within the indicated antigenic site, clearly show that substitutions outside the site, and which by design are not part of the site, can influence very markedly the reactivity of the protein variant with the anti-site mAbs. The approach can, therefore, lead to serious errors if used to identify residues of protein antigenic sites.

Effects of amino acid substitutions outside an antigenic site on protein binding to monoclonal antibodies of predetermined specificity obtained by peptide immunization: demonstration with region 145-151 (antigenic site 5) of myoglobin

Monoclonal antibodies of predetermined specificity were prepared by immunization with a free (i.e., without coupling to any protein carrier) synthetic peptide representing region 145-151 of sperm whale myoglobin (SpMb) and their cross-reactions with eight Mb variants were determined. Five Mbs--bottle-nose dolphin myoglobin (BdMb), pacific common dolphin myoglobin (PdMb), horse myoglobin (HsMb), dog myoglobin (DgMb), and badger myoglobin (BgMb)--have an identical sequence in that region. Nevertheless, these Mbs exhibited very different cross-reactivities. BdMb and PdMb exhibited cross-activities which were comparable to that of the reference antigen, SpMb; while the reactivity of HsMb was remarkedly decreased, DgMb and BgMb showed almost no cross-reactions with these mAbs. Since the region 145-151 has an identical sequence in all the five Mbs, it is concluded that the differences in their antigenic reactivities with anti-region 145-151 mAbs are due to the effects of amino acid substitutions outside the region 145-151. Another pair of myoglobins, echidna myoglobin (EdMb) and chicken myoglobin (ChMb), have the same sequence in that region, but reacted very differently with anti-region 145-151 mAbs. The reactivity and affinity of EdMb were substantially decreased while those of ChMb were almost completely absent, relative to SpMb. It is concluded, contrary to popular assumptions, that when an amino acid substitution influences the binding of a protein variant to a mAb, it is not necessary for that substitution to be an actual contact residue (i.e., a residue within the antigenic site where the mAb binds). Such effects, which are often very drastic, could be due to indirect influences of the substitution on the chemical and binding properties of the site residues. Furthermore, residues which had been postulated, on the basis of these assumptions, to constitute discontinuous antigenic sites in SpMb, were found [from the present studies and those recently reported with mAbs against the other four antigenic site of Mb (regions 15-22, 56-62, 94-100, and 113-120 of SpMb)] to merely be exerting indirect effects on the known five antigenic sites of Mb. The effects of substitutions, which can happen even in the absence of conformational changes, are determined by many factors, such as the chemical nature of the substitution, its environment, its distance from the site, and the nature of the site residue(s) being affected.

Effects of amino acid substitutions outside an antigenic site on protein binding to monoclonal antibodies of predetermined specificity obtained by peptide immunization: demonstration with region 56-62 (antigenic site 2) of myoglobin

This work was carried out in order to study the effects of substitutions outside antigenic site 2 of sperm whale myoglobin (SpMb) on the reactivity of protein variants with antisite 2 monoclonal antibodies (mAbs). A synthetic peptide corresponding to region 56-62 (site 2) of SpMb was used as an immunogen in mice in its free form (i.e., without coupling to any carrier) to prepare a panel of mAbs whose predetermined specificity is directed, by design, against this region. The binding of three of these mAbs to eight Mbs from different species was studied. Myoglobins of Pacific common dolphin, finback whale, and horse, which have no substitutions within region 56-62 relative to SpMb, showed remarkable differences in their cross-reactivities and relative affinities with each of the mAbs. Myoglobins of badger, chicken, and dog, although they have an identical substitution within the site (Ala-57 to Gly), exhibited cross-reactivities with a given mAb that were affected differently. Echidna Mb, which has one replacement (Glu-59 to Ala) within region 56-62, displayed greatly reduced cross-reactivities and relative binding affinities. The results, especially those from Mbs that have no substitutions within the boundaries of site 2, clearly indicate that substitutions outside site 2 of Mb can exert drastic effects on the binding of the Mb variants with mAbs whose specificity was predesigned to be against the site. These indirect effects and their impact on site reactivity will completely explain previous findings on cross-reactivities of Mb variants with mAbs of unknown specificity and will rule out the postulations of discontinuous sites in Mb, which were based on the assumption that every substitution affecting reactivity is directly involved in binding to antibody.