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Binding, tuning and mechanical function of the 4-hydroxy-cinnamic acid chromophore in photoactive yellow protein

Author: Horst, M.A. van der · Arents, J.C. · Kort, R. · Hellingwerf, K.J.
Institution: TNO Kwaliteit van Leven
Source:Photochemical and Photobiological Sciences, 5, 6, 571-579
Identifier: 239979
doi: doi:10.1039/b701072a
Keywords: Biology · Biotechnology · 4 hydroxy cinnamic acid · apoprotein · cinnamic acid derivative · coumaric acid · cysteine · glycine · mutant protein · photoactive yellow protein · protein · sinapic acid · thiomethyl 4 coumaric acid · article · catalysis · chemical binding · chromatophore · color · covalent bond · in vitro study · knowledge · model · photochemistry · pKa · point mutation · priority journal · protein binding · protein function · protein modification · protein variant · proton transport · Bacterial Proteins · Coumaric Acids · Hydrogen-Ion Concentration · Photoreceptors, Microbial · Point Mutation · Protein Binding · Spectrophotometry, Ultraviolet · Bacteria (microorganisms)


The bacterial photoreceptor protein photoactive yellow protein (PYP) covalently binds the chromophore 4-hydroxy coumaric acid, tuning (spectral) characteristics of this cofactor. Here, we study this binding and tuning using a combination of pointmutations and chromophore analogs. In all photosensor proteins studied to date the covalent linkage of the chromophore to the apoprotein is dispensable for light-induced catalytic activation. We analyzed the functional importance of the covalent linkage using an isosteric chromophore-protein variant in which the cysteine is replaced by a glycine residue and the chromophore by thiomethyl-p-coumaric acid (TMpCA). The model compound TMpCA is shown to weakly complex with the C69G protein. This non-covalent binding results in considerable tuning of both the pKa and the color of the chromophore. The photoactivity of this system, however, was strongly impaired, making PYP the first known photosensor protein in which the covalent linkage of the chromophore is of paramount importance for the functional activity of the protein in vitro. We also studied the influence of chromophore analogs on the color and photocycle of PYP, not only in WT, but especially in the E46Q mutant, to test if effects from both chromophore and protein modifications are additive. When the E46Q protein binds the sinapinic acid chromophore, the color of the protein is effectively changed from yellow to orange. The altered charge distribution in this protein also results in a changed pKa value for chromophore protonation, and a strongly impaired photocycle. Both findings extend our knowledge of the photochemistry of PYP for signal generation. © The Royal Society of Chemistry and Owner Societies.