Cross-reactive binding of cyclic peptides to an anti-TGFalpha antibody fab fragment: an X-ray structural and thermodynamic analysis

Item Type:	Article
Title:	Cross-reactive binding of cyclic peptides to an anti-TGFalpha antibody fab fragment: an X-ray structural and thermodynamic analysis
Creators Name:	Hahn, M. and Winkler, D. and Welfle, K. and Misselwitz, R. and Welfle, H. and Wessner, H. and Zahn, G. and Scholz, C. and Seifert, M. and Harkins, R. and Schneider-Mergener, J. and Hoehne, W.G.
Abstract:	The monoclonal antibody tAb2 binds the N-terminal sequence of transforming growth factor α, VVSHFND. With the help of combinatorial peptide libraries it is possible to find homologous peptides that bind tAb2 with an affinity similar to that of the epitope. The conformational flexibility of short peptides can be constrained by cyclization in order to improve their affinity to the antibody and their stability towards proteolysis. Two cyclic peptides which are cross-reactive binders for tAb2 were selected earlier using combinatorial peptide libraries. One is cyclized by an amide bond between the N-alpha group and the side-chain of the last residue (cyclo-SHFNEYE), and the other by a disulfide bridge (cyclo-CSHFNDYC). The complex structures of tAb2 with the linear epitope peptide VVSHFND and with cyclo-SHFNEYE were determined by X-ray diffraction. Both peptides show a similar conformation and binding pattern in the complex. The linear peptide SHFNEYE does not bind tAb2, but cyclo-SHFNEYE is stabilized in a loop conformation suitable for binding. Hence the cyclization counteracts the exchange of aspartate in the epitope sequence to glutamate. Isothermal titration calorimetry was used to characterize the binding energetics of tAb2 with the two cyclic peptides and the epitope peptide. The binding reactions are enthalpically driven with an unfavorable entropic contribution under all measured conditions. The association reactions are characterized by negative ΔC p changes and by the uptake of one proton per binding site. A putative candidate for proton uptake during binding is the histidine residue in each of the peptides. Hydrogen bonds and the putative formation of an electrostatic pair between the protonated histidine and a carboxy group may contribute markedly to the favorable enthalpy of complex formation. Implications to cyclization of peptides for stabilization are discussed.
Keywords:	Antibody Cross-Reactivity, Cyclic Peptides, Isothermal Titration Calorimetry, Peptide Library, Transforming Growth Factor {Alpha}, Animals, Mice
Source:	Journal of Molecular Biology
ISSN:	0022-2836
Publisher:	Elsevier
Volume:	314
Number:	2
Page Range:	293-309
Date:	1 January 2001
Official Publication:	https://doi.org/10.1006/jmbi.2001.5135
PubMed:	View item in PubMed

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