Benzophenone Photophore Flexibility and Proximity: Molecular and Crystal Structure of a Bpa-Containing Trichogin Dodecapeptide Analogue

An X-ray diffraction analysis of a Bpa-containing analogue of the lipopeptaibol trichogin GA IV strongly points to the conclusion that caution should be exercised in utilizing this highly flexible, benzophenone-based photoprobe acritically in biochemical and biophysical studies. As a result of the different side-chain conformations adopted by the Bpa residue, the distance of its ketone carbonyl carbon from the midpoint of the N-O bond of the nitroxide-containing side chain of the TOAC residue in the two crystallographically independent peptide molecules differs by as much as 11 Å.