TY - JOUR T1 - The unique protein-to-protein carotenoid transfer mechanism JF - bioRxiv DO - 10.1101/127183 SP - 127183 AU - E.G. Maksimov AU - N.N. Sluchanko AU - Y.B. Slonimskiy AU - K.S. Mironov AU - K.E. Klementiev AU - M. Moldenhauer AU - T. Friedrich AU - D.A. Los AU - V.Z. Paschenko AU - A.B. Rubin Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/04/13/127183.abstract N2 - OCPOrange Carotenoid ProteinNTDN-terminal domain of OCPCTDC-terminal domain of OCPCOCPC-terminal OCP-related Carotenoid-binding ProteinCOCP-W288ACOCP with a Ala substitution of TrpGFPenhanced Green Fluorescence ProteinFRPFluorescence Recovery ProteinNTEN-terminal extension (comprising the αA helix up to amino acid 20)ΔNTEOCP with the 20 most N-terminal amino acids deleted (OCPΔ2-20)ECNEchinenoneCANCanthaxanthinALActinic LightAbstract Orange Carotenoid Protein (OCP) is known to be an effector and regulator of cyanobacterial photoprotection. This 35 kDa water-soluble protein provides specific environment for keto-carotenoids, the excitation of which induced by the absorption of blue-green light causes dramatic but fully reversible rearrangements of the OCP structure, including carotenoid translocation and separation of C- and N-terminal domains upon transition from the basic orange to photoactivated red OCP form. While recent studies significantly improved our understanding of the OCP photocycle and interaction with phycobilisomes and the fluorescence recovery protein, the mechanism of OCP assembly remains unclear. Apparently, this process requires targeted delivery and incorporation of a highly hydrophobic carotenoid molecule into the water-soluble apoprotein of OCP. Recently, we introduced a novel carotenoid carrier protein, COCP, which consists of dimerized C-domain(s) of OCP and can combine with the isolated N-domain to form transient OCP-like species. Here, we demonstrate that in vitro COCP efficiently transfers otherwise tightly bound carotenoid to the full-length OCP apoprotein, resulting in formation of the photoactive OCP from completely photoinactive species. We accurately analyze peculiarities of this carotenoid transfer process which, to the best of our knowledge, seems unique, previously uncharacterized protein-to-protein carotenoid transfer process. We hypothesize that a similar OCP assembly can occur in vivo, substantiating specific roles of the COCP carotenoid carrier in cyanobacterial photoprotection.OCPOrange Carotenoid ProteinNTDN-terminal domain of OCPCTDC-terminal domain of OCPCOCPC-terminal OCP-related Carotenoid-binding ProteinCOCP-W288ACOCP with a Ala substitution of TrpGFPenhanced Green Fluorescence ProteinFRPFluorescence Recovery ProteinNTEN-terminal extension (comprising the αA helix up to amino acid 20)ΔNTEOCP with the 20 most N-terminal amino acids deleted (OCPΔ2-20)ECNEchinenoneCANCanthaxanthinALActinic Light ER -