Redder Than Red

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Science  07 Dec 2012:
Vol. 338, Issue 6112, pp. 1299-1300
DOI: 10.1126/science.1231589

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A chromophore is the part of a molecule that imparts its color. Arguably the most common chromophores in biology are carotenoids such as retinoids. Their absorption spectra can be tuned across a wide range of light energy by modulating the electronic environment within the protein to which they are attached. On page 1340 of this issue, Wang et al. (1) report a systematic study of the spectral tuning of an engineered all-trans-retinal pigment within a protein environment. Using protein engineering and x-ray crystallography, they create a palette of retinal-based pigments that reveal how electrostatics dominates spectral tuning (see the figure).