01859nas a2200241   4500008004500000020001400045245011000059210006900169260000800238300001400246490000800260520114300268653001501411100002101426700001501447700001601462700001301478700001901491700002201510700001601532700002001548856004901568       2020                        Engldsh    a0006-349500aEvidence of Intramolecular Structural Stabilization in Light Activated State of Orange Carotenoid Protein0 aEvidence of Intramolecular Structural Stabilization in Light Act  cFeb  a208A-208A0 v1183 a<p style="text-align: justify;">Orange carotenoid protein (OCP) controls efficiency of the light harvesting antenna, the phycobilisome (PBS), in diverse cyanobacteria and prevents oxidative damage. It is the only known photoactive protein that uses a carotenoid, canthaxanthin, as its chromophore. The structure of OCP consists of two globular domains, connected by an unstructured loop, that forms a hydrophobic pocket for the carotenoid. In low light, canthaxanthin bound OCP is inactive and appears orange. Illumination by strong light results in an active state that interacts with the PBS to induce fluorescence quenching, a red appearance and conformational changes that include a 12Å shift by canthaxanthin into the N-terminal domain. Terahertz (THz) dynamical transition measurements and anisotropic terahertz microscopy are used to measure the intramolecular structural dynamics in the inactive and active states, which can be induced by photoexcitation or chaotropic salts. The measurements indicate that the active state has a decrease in structural flexibility, which may be related to enhanced interactions with the PBS.</p>10aBiophysics1 aMcKinney, J., A.1 aSharma, A.1 aCrossen, K.1 aDeng, Y.1 aGeorge, D., K.1 aLechno-Yossef, S.1 aKerfeld, C.1 aMarkelz, A., G.  uhttps://markelz.physics.buffalo.edu/node/25301881nas a2200181   4500008004100000245009900041210006900140260001600209520131100225100001701536700001501553700001301568700001501581700002201596700001601618700001601634856004901650       2020                        eng d00aStabilization of Terahertz Vibrational Modes in Illuminated Orange Carotenoid Protein Crystals0 aStabilization of Terahertz Vibrational Modes in Illuminated Oran  aBuffalo, NY3 a<p class="rtejustify">Orange carotenoid protein (OCP) controls efficiency of the phycobilisome (PBS), the light harvesting antenna in cyanobacteria, to prevent oxidative damage. The OCP switches from resting state to photo protective state with intense blue light illumination. Questions persist as to why OCPR interaction increases with the PBS over that with the OCPO. Here we examine the role of long-range intramolecular vibrations within OCP. Using Stationary Sample Anisotropic Terahertz Microscopy (SSATM) we measure changes in the intramolecular vibrations with photo switching. We report the first observation of switching in the intramolecular vibrations with photoexcitation. Results suggest that there is a stiffening of the molecule in the photo protective state. This increase in structural stability may enhance the interaction with the PBS change in OCP interaction with PBS. In low light, carotenoid bound OCP appears orange (OCP <sup>o</sup> ) and is inactive. Illumination by strong light converts OCP to the active, red (OCPR) state, which interacts with the PBS. A comparison of anisotropic THz microscopy measurements of dark adapted (OCP <sup>o</sup> ) and illuminated OCP crystals indicate differences in their vibrational modes that may be important for OCP-PBS interactions.</p>
1 aMcKinney, J.1 aSharma, A.1 aDeng, Y.1 aGeorge, D.1 aLechno-Yossef, S.1 aKerfeld, C.1 aMarkelz, A.  uhttps://markelz.physics.buffalo.edu/node/544