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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The orange carotenoid protein (OCP) is a structurally and functionally modular photoactive protein involved in cyanobacterial photoprotection. Using phylogenomic analysis, we have revealed two new paralogous OCP families, each distributed among taxonomically diverse cyanobacterial genomes. Based on bioinformatic properties and phylogenetic relationships, we named the new families OCP2 and OCPx to distinguish them from the canonical OCP that has been well characterized in Synechocystis, denoted hereafter as OCP1. We report the first characterization of a carotenoprotein photoprotective system in the chromatically acclimating cyanobacterium Tolypothrix sp. PCC 7601, which encodes both OCP1 and OCP2 as well as the regulatory fluorescence recovery protein (FRP). OCP2 expression could only be detected in cultures grown under high irradiance, surpassing expression levels of OCP1, which appears to be constitutive; under low irradiance, OCP2 expression was only detectable in a Tolypothrix mutant lacking the RcaE photoreceptor required for complementary chromatic acclimation. In vitro studies show that Tolypothrix OCP1 is functionally equivalent to Synechocystis OCP1, including its regulation by Tolypothrix FRP, which we show is structurally similar to the dimeric form of Synechocystis FRP. In contrast, Tolypothrix OCP2 shows both faster photoconversion and faster back-conversion, lack of regulation by the FRP, a different oligomeric state (monomer compared to dimer for OCP1) and lower fluorescence quenching of the phycobilisome. Collectively, these findings support our hypothesis that the OCP2 is relatively primitive. The OCP2 is transcriptionally regulated and may have evolved to respond to distinct photoprotective needs under particular environmental conditions such as high irradiance of a particular light quality, whereas the OCP1 is constitutively expressed and is regulated at the post-translational level by FRP and/or oligomerization.
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PMID:Additional families of orange carotenoid proteins in the photoprotective system of cyanobacteria. 2869 21

The orange carotenoid protein (OCP) is a structurally and functionally modular photoactive protein involved in cyanobacterial photoprotection. Recently, based on bioinformatic analysis and phylogenetic relationships, new families of OCP have been described, OCP2 and OCPx. The first characterization of the OCP2 showed both faster photoconversion and back-conversion, and lower fluorescence quenching of phycobilisomes relative to the well-characterized OCP1. Moreover, OCP2 is not regulated by the fluorescence recovery protein (FRP). In this work, we present a comprehensive study combining ultrafast spectroscopy and structural analysis to compare the photoactivation mechanisms of OCP1 and OCP2 from Tolypothrix PCC 7601. We show that despite significant differences in their functional characteristics, the spectroscopic properties of OCP1 and OCP2 are comparable. This indicates that the OCP functionality is not directly related to the spectroscopic properties of the bound carotenoid. In addition, the structural analysis by X-ray footprinting reveals that, overall, OCP1 and OCP2 have grossly the same photoactivation mechanism. However, the OCP2 is less reactive to radiolytic labeling, suggesting that the protein is less flexible than OCP1. This observation could explain fast photoconversion of OCP2.
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PMID:Comparative ultrafast spectroscopy and structural analysis of OCP1 and OCP2 from Tolypothrix. 3173 94