PDBsum entry 5tux

Carotenoid binding protein

PDB id: 5tux

Contents

Protein chain

305 a.a.

Ligands

ECH

GOL

Waters ×268

PDB id:

5tux

Name:

Carotenoid binding protein

Title:

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

Structure:

Orange carotenoid-binding protein. Chain: a. Synonym: ocp. Engineered: yes

Source:

Synechocystis sp. (Strain pcc 6803 / kazusa). Organism_taxid: 1111708. Strain: pcc 6803 / kazusa. Gene: slr1963. Expressed in: escherichia coli. Expression_system_taxid: 511693.

Resolution:

1.50Å R-factor: 0.151 R-free: 0.181

Authors:

X.Yang,S.Bandara,Z.Ren

Key ref:

S.Bandara et al. (2017). Photoactivation mechanism of a carotenoid-based photoreceptor. Proc Natl Acad Sci U S A, 114, 6286-6291. PubMed id: 28559328

Date:

07-Nov-16 Release date: 07-Jun-17

Protein chain

P74102  (OCP_SYNY3) -  Orange carotenoid-binding protein from Synechocystis sp. (strain PCC 6803 / Kazusa)

Seq: 317 a.a.

Struc: 305 a.a.

Proc Natl Acad Sci U S A 114:6286-6291 (2017)

PubMed id: 28559328

Photoactivation mechanism of a carotenoid-based photoreceptor.

S.Bandara, Z.Ren, L.Lu, X.Zeng, H.Shin, K.H.Zhao, X.Yang.

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.