Molecular Recognition and Signal Transduction in Antibodie

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An isotope-edited nuclear magnetic resonance study is reported of the Fv fragment, which is the smallest antigen recognition unit composed of V_H and V_L domains. The Fv fragment has been obtained by clostripain digestion of a short-chain anti-dansyl mouse IgG2a monoclonal antibody. A variety of stable-isotope labeled anti-dansyl Fv analogues have been prepared. On the basis of stable isotope-aided heteronuclear and homonuclear two-dimensional NMR spectra, it has been concluded that 1) the dansylring is bound through Tyr-96H and Tyr-104H to both ends of H3 loop, the third hypervariable region of the heavy chain, 2) in the absence of DNS-Lys, the H3 loop displays a significant degree of internal motion and 3) binding of DNS-Lys induces a significant change in the dynamical structure of the H3 loop.