Exploring the dynamic nature of OCP crystals by combined use of diffraction and in crystallo spectrophotometry at room-temperature.

The photoactive Orange Carotenoid Protein (OCP) is a reversible photoswitch which serves photoprotection in cyanobacteria (Wilson et al. 2006). OCP is functionalized by a keto-carotenoid pigment which, in the presence of a blue-green photon, is able to induce conformational changes resulting in a photoactivated state capable of quenching an excess of absorbed light energy. Preliminary experiments offered first evidence that dehydration of OCP crystals lead to the trapping of a pre-activated state. The very goal of our experiment is to verify this hypothesis by simultaneous collection of diffraction and spectroscopic data from crystals at room-temperature and at varied levels of humidity.