K. Welfle et al., Interaction of a designed interleukin-10 epitope mimic with an antibody studied by isothermal titration microcalorimetry, J MOL RECOG, 14(2), 2001, pp. 89-98
The mechanism of recognition of proteins and peptides by antibodies and the
factors determining binding affinity and specificity are mediated by essen
tially the same features. However, additional effects of the usually unfold
ed and flexible solution structure of peptide ligands have to be considered
. In an earlier study we designed and optimized six peptides (pepI to pepVI
) mimicking the discontinuous binding site of interleukin-10 for the anti-i
nterleukin-10 monoclonal antibody (mab) CB/RS/1, Three of them were selecte
d for analysis of their solution conformation by circular dichroism measure
ments. The peptides differ in the content of alpha -helices and in the indu
cibility of helical secondary structures by trifluoroethanol, These propert
ies, however, do not correlate with the binding affinity. PepVI, a 32-mer c
yclic epitope mimic, has the highest affinity to mab CB/RS/1 identified to
date. CD difference spectroscopy suggests an increase of the alpha -helix c
ontent of pepVI with complex formation. Binding of pepVI to mab CB/RS/1 is
characterized by a large negative, favorable binding enthalpy and a smaller
unfavorable loss of entropy (DeltaH degrees = -16.4 kcal mol(-1), T DeltaS
degrees = -6.9 kcal.mol(-1)) resulting in DeltaG degrees = -9.15 kcal.mol(
-1) at 25 degreesC as determined by isothermal titration calorimetry. Bindi
ng of pepVI is enthalpically driven over the entire temperature range studi
ed (10-35 degreesC). Complex formation is not accompanied by proton uptake
or release. A negative heat capacity change DeltaC(p) of -0.354 kcal.mol(-1
).K-1 was determined from the temperature dependence of DeltaH degrees. The
selection of protein mimics with the observed thermodynamic properties is
promoted by the applied identification and iterative optimization procedure
. Copyright (C) 2001 John Wiley & Sons, Ltd.