Probing A Protein’s Elusive Chromophore

A study of p-coumaric acid reveals for the first time the spectral characteristics of this important chromophore (J. Am. Chem. Soc., DOI: 10.1021/ja101668v). The results begin to unravel the processes that drive the much-investigated photocycle of the bacterial photoreceptor known as photoactive yellow protein (PYP), in which p-coumaric acid plays a key role. Although chemists believe that the cycle begins with photoinitiated trans-to-cis isomerization of p-coumaric acid, that hypothesis has never been verified. Wybren J. Buma of the University of Amsterdam and colleagues have now used high-resolution excitation and absorption spectra coupled with density functional theory to show that the molecule does indeed undergo this transformation. The findings may “serve as an excellent point of reference for further elucidation” of the PYP system, and photosensory proteins in general, Buma and coworkers write.