5TUX

crystal structure and light induced structural changes in orange carotenoid protein bound with echinenone

Summary for 5TUX

• Entry DOI: 10.2210/pdb5tux/pdb
• Related: 5TUW 5TV0
• Descriptor: Orange carotenoid-binding protein, beta,beta-caroten-4-one, GLYCEROL, ... (4 entities in total)
• Functional Keywords: photoreceptors, photoprotection, dynamic crystallography, carotenoid binding protein
• Biological source: Synechocystis sp. (strain PCC 6803 / Kazusa)
• Total number of polymer chains: 1
• Total formula weight: 36156.43

Authors

Yang, X.,Bandara, S.,Ren, Z. (deposition date: 2016-11-07, release date: 2017-06-07, Last modification date: 2023-10-04)

Primary citation

Bandara, S.,Ren, Z.,Lu, L.,Zeng, X.,Shin, H.,Zhao, K.H.,Yang, X.
Photoactivation mechanism of a carotenoid-based photoreceptor.
Proc. Natl. Acad. Sci. U.S.A., 114:6286-6291, 2017

PubMed Abstract: Photoprotection is essential for efficient photosynthesis. Cyanobacteria have evolved a unique photoprotective mechanism mediated by a water-soluble carotenoid-based photoreceptor known as orange carotenoid protein (OCP). OCP undergoes large conformational changes in response to intense blue light, and the photoactivated OCP facilitates dissipation of excess energy via direct interaction with allophycocyanins at the phycobilisome core. However, the structural events leading up to the OCP photoactivation remain elusive at the molecular level. Here we present direct observations of light-induced structural changes in OCP captured by dynamic crystallography. Difference electron densities between the dark and illuminated states reveal widespread and concerted atomic motions that lead to altered protein-pigment interactions, displacement of secondary structures, and domain separation. Based on these crystallographic observations together with site-directed mutagenesis, we propose a molecular mechanism for OCP light perception, in which the photochemical property of a conjugated carbonyl group is exploited. We hypothesize that the OCP photoactivation starts with keto-enol tautomerization of the essential 4-keto group in the carotenoid, which disrupts the strong hydrogen bonds between the bent chromophore and the protein moiety. Subsequent structural changes trapped in the crystal lattice offer a high-resolution glimpse of the initial molecular events as OCP begins to transition from the orange-absorbing state to the active red-absorbing state.

PubMed: 28559328
DOI: 10.1073/pnas.1700956114

Experimental method

X-RAY DIFFRACTION (1.5 Å)