The "lamin B-fold". Anti-idiotypic antibodies reveal a structural complementarity between nuclear lamin B and cytoplasmic intermediate filament epitopes.
Previous studies have shown that nuclear lamin B binds specifically to the C-terminal domains of type III intermediate filament (IF) proteins under in vitro conditions. To further explore such site-specific interactions, we have used a two-step anti-idiotypic antibody approach. First, a monoclonal antibody disrupting the cytoplasmic IF network organization of living cells (mAb7A3) (Matteoni, R., and Kreis, T. E. (1987) J. Cell Biol. 105, 1253-1265) was characterized. Epitope mapping demonstrated that this antibody recognized a site located in the C-terminal domains of vimentin and peripherin (type III IF proteins). mAb7A3 was able to inhibit more than 80% of the in vitro binding of nuclear lamin B to PI, a synthetic peptide modeled after the C-terminal domain of peripherin that comprises a lamin B-binding site (Djabali, K., Portier, M. M., Gros, F., Blobel, G., and Georgatos, S. D. (1991) Cell 64, 109-121). In a second step, animals were immunized with mAb7A3 and the resulting anti-idiotypic sera were screened. Two of these antisera reacted specifically with nuclear lamin B but not with type A lamins or cytoplasmic IF proteins. The anti-lamin B activity of one of the antisera was isolated by affinity chromatography using a lamin B-agarose matrix. The reaction of these affinity-purified antibodies with lamin B was inhibited by mAb7A3. Furthermore, the anti-lamin B antibodies reacted with Fab fragments of mAb7A3 and abolished binding of lamin B to PI. From these data we conclude that anti-idiotypic antibodies against the paratope of mAb7A3 recognize specific epitopes of the lamin B molecule that have shapes complementary to the one of the C-terminal domain of type III IF proteins. We speculate that these (regional) conformations, which we term the "lamin B-fold," may also occur in non-lamin proteins that mediate the anchorage of IFs to various membranous organelles.
Papamarcaki
T
T
Program of Cell Biology, European Molecular Biology Laboratory, Heidelberg, Federal Republic of Germany.
Kouklis
P D
PD
Kreis
T E
TE
Georgatos
S D
SD
D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000276:immunology; D000939:Epitopes; D007381:Intermediate Filament Proteins / Q000276:immunology / Q000648:ultrastructure*; D034921:Lamin Type B; D034882:Lamins; D008562:Membrane Glycoproteins; D051379:Mice; D009419:Nerve Tissue Proteins; D015530:Nuclear Matrix / Q000648:ultrastructure; D009687:Nuclear Proteins / Q000276:immunology / Q000648:ultrastructure*; D064531:Peripherins; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D014746:Vimentin / Q000276:immunology
D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal; D000939:Epitopes; D007381:Intermediate Filament Proteins; D034921:Lamin Type B; D034882:Lamins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D064531:Peripherins; D014746:Vimentin