### Structural studies of anti-tumour antibody R24.

##### Description
 Title: Structural studies of anti-tumour antibody R24. Authors: Kaminski, Marcin Jerzy. Date: 1998 Abstract: The murine monoclonal antibody R24 and mouse-human Fv-IgG1($\kappa)$ chimeric monoclonal antibody chR24 are specific for the cell surface tumour antigen disialoganglioside GD3. X-ray diffraction and surface plasmon resonance experiments have been employed to study the mechanism of "homophilic binding" in which molecules of R24 recognize and bind to other molecules of R24 through the heavy chain variable domains. The relationship between GD3-binding and the homophilic-binding domain, and the mechanism of the behaviour of chR24 mutants has also been investigated. R24 exhibits strong binding to GD3-bearing liposomes, with no apparent binding saturation, while chR24 binding is much weaker. This suggests that cooperative interactions involving antibody constant regions contribute to R24 binding to membrane-anchored GD3. The crystal structures of the Fabs from R24 and chR24 reveal the mechanism for homophilic binding and confirm that the homophilic and antigen-binding idiotopes are distinct. The homophilic binding idiotope is formed largely by an antiparallel $\beta$-sheet dimerization between the H2 CDR loops of two Fabs, while the antigen-binding idiotope is a pocket formed by the three CDR loops of the heavy chain. The conformation of the antigen-binding site explains why mutations of specific residues blocks GD3-binding. Comparison with known structures of other Fabs shows that the formation of homophilic dimers requires the presence of a canonical conformation for the H2 CDR in conjunction with side chain participation. The relative positions of the homophilic and antigen binding sites allows for a lattice of R24 antibodies to be constructed, which is stabilized by the presence of the cell membrane. The model provides for the selective recognition cells which overexpress GD3 on the membrane surface by R24. URL: http://hdl.handle.net/10393/4410 Collection Thèses, 1910 - 2010 // Theses, 1910 - 2010