SUNY at Albany
June 19-23, 2001
Interaction of a designed interleukin-10 epitope mimic with an antibody studied by isothermal titration microcalorimetry
For the recognition of peptides by antibodies the usually unfolded and flexible solution structure of peptide ligands is of considerable importance. Three earlier designed peptides (1) mimicking the discontinuous binding site of interleukin-10 for the anti-interleukin-10 monoclonal antibody (mab) CB/RS/1 were analyzed by circular dichroism measurements. The peptides differ in the content of a-helices and in the inducibility of helical secondary structures by trifluoroethanol but these properties do not correlate with the binding affinity. For the strongly binding pepVI, a 32-mer cyclic epitope mimic, CD difference spectroscopy suggests an increase of the helix content with complex formation. Binding of pepVI to mab CB/RS/1 is enthalpically driven over the entire temperature range studied (10 to 35°C), and characterized by a large negative, favorable binding enthalpy and an unfavorable, but smaller loss of entropy ( DH° = -16.4 kcal'mol-1, TDS° = -kcal'mol-1) resulting in DG° = -9.5 kcal'mol-1 at 25°C (2). Complex formation is not accompanied by proton uptake or release. A negative heat capacity change DCp of -0.354 kcal'mol-1K-1 was determined from the temperature dependence of DH°. The selection of protein mimics with the observed thermodynamic properties is promoted by the applied identification and iterative optimization procedure (1).
Supported by DFG grants He1318/17-1 and FOR299/1-2.References and Footnotes
Karin Welfle (1), Rolf Misselwitz (1,3), Robert Sabat (2),Hans-Dieter Volk (2),
Max-Delbrück-Centrum für Molekulare Medizin (1), Berlin; Institut für Medizinische Immunologie (2) and Institut für Biochemie (3), Universitätsklinikum Charité, Humboldt-Universität zu Berlin; JERINI Bio Tools GmbH (4), Ost-West-Zentrum, Berlin, Germany.