Benzophenone photophore flexibility and proximity: molecular and crystal-state structure of a bpa-containing trichogin dodecapeptide analogue.

The three-dimensional structure and the conformational behavior of a para-benzoylphenylalanine (Bpa) contg. trichogin dodecapeptide analog were evaluated using an X-ray diffraction anal. Results strongly support the view that, despite the unquestionable usefulness of the Bpa residue as a photoprobe, caution is needed in extrapolating the anal. results of photo crosslinking expts. and photophys. data to Bpa proximity, i.e., to protein mapping and intramol. distances, resp. It is also important to remember that peptide ligands quite often show a much reduced conformational flexibility when bound to a protein receptor site. The Bpa residue adopts a backbone conformation close to the b-sheet structure, and more importantly, its side chain is rigidified to the g- conformation because the bulky arom. residue occupies a largely hydrophobic patch in the interior of the enzyme.