title: Mass spectrometry footprinting reveals the structural rearrangements of  cyanobacterial orange carotenoid protein upon light activation.
abstract: The orange carotenoid protein (OCP), a member of the family of blue light photoactive proteins, is required for efficient photoprotection in many cyanobacteria. Photoexcitation of the carotenoid in the OCP results in structural changes within the chromophore and the protein to give an active red form of OCP that is required for phycobilisome binding and consequent fluorescence quenching. We characterized the light-dependent structural changes by mass spectrometry-based carboxyl footprinting and found that an α helix in the N-terminal extension of OCP plays a key role in this photoactivation process. Although this helix is located on and associates with the outside of the β-sheet core in the C-terminal domain of OCP in the dark, photoinduced changes in the domain structure disrupt this interaction. We propose that this mechanism couples light-dependent carotenoid conformational changes to global protein conformational dynamics in favor of functional phycobilisome binding, and is an essential part of the OCP photocycle.
authors.affiliation: Department of Biology, Washington University in St. Louis, MO 63130, USA; Department of Chemistry, Washington University in St. Louis, MO 63130, USA; Photosynthetic Antenna Research Center (PARC), Washington University in St. Louis, MO 63130, USA. Electronic address: hliu6@wustl.edu.
authors.forename: Haijun
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Chemistry, Washington University in St. Louis, MO 63130, USA; Photosynthetic Antenna Research Center (PARC), Washington University in St. Louis, MO 63130, USA.
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Biology, Washington University in St. Louis, MO 63130, USA; Photosynthetic Antenna Research Center (PARC), Washington University in St. Louis, MO 63130, USA.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: King
authors.affiliation: Photosynthetic Antenna Research Center (PARC), Washington University in St. Louis, MO 63130, USA.
authors.forename: Nathan R
authors.initials: NR
authors.lastname: Wolf
authors.affiliation: Department of Biology, Washington University in St. Louis, MO 63130, USA; Photosynthetic Antenna Research Center (PARC), Washington University in St. Louis, MO 63130, USA.
authors.forename: Mindy
authors.initials: M
authors.lastname: Prado
authors.affiliation: Department of Chemistry, Washington University in St. Louis, MO 63130, USA; Photosynthetic Antenna Research Center (PARC), Washington University in St. Louis, MO 63130, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Gross
authors.affiliation: Department of Biology, Washington University in St. Louis, MO 63130, USA; Department of Chemistry, Washington University in St. Louis, MO 63130, USA; Photosynthetic Antenna Research Center (PARC), Washington University in St. Louis, MO 63130, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Blankenship
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002234:Carbodiimides / Q000737:chemistry / Q000378:metabolism; D005998:Glycine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D008027:Light; D013058:Mass Spectrometry / Q000379:methods*; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D045524:Phycobilisomes / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation / Q000528:radiation effects; D023302:Protein Footprinting / Q000379:methods; D017433:Protein Structure, Secondary / Q000528:radiation effects*; D017434:Protein Structure, Tertiary / Q000528:radiation effects; D013053:Spectrophotometry; D046939:Synechocystis / Q000378:metabolism; D013997:Time Factors
chemical_list: C518491:1-ethyl-3-(3-(diethylamino)propyl)carbodiimide; D001426:Bacterial Proteins; D002234:Carbodiimides; D010455:Peptides; D045524:Phycobilisomes; C109473:orange carotenoid protein, Synechocystis; C022010:glycine ethyl ester; D005998:Glycine