THIOL ESTER-LINKED P-COUMARIC ACID AS A NEW PHOTOACTIVE PROSTHETIC GROUP IN A PROTEIN WITH RHODOPSIN-LIKE PHOTOCHEMISTRY

A number of Eubacteria contain a photoactive yellow protein which has a photosensory function in negative phototaxis. It has been proposed t hat the cofactor responsible for the intense yellow color of this prot ein is retinal [McRee, D. E., et al. (1989) Proc. Natl. Acad. Sci. U.S .A. 86, 6533-6537]. This would make it the first eubacterial rhodopsin . Here we report the chemical structure of this chromophoric group to be p-coumaric acid, which is covalently bound to a unique cysteine in the apoprotein via a thiol ester bond, and thus not retinal. This make s PYP the first example of a protein containing p-coumaric acid, a met abolite previously found only in plants, as a prosthetic group and est ablishes the photoactive yellow proteins as a new type of photochemica lly active receptor molecule.