01881nas 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/54402599nas a2200205   4500008004500000020001400045245005800059210005800117260000800175300001400183490000800197520204200205653001502247100001702262700001702279700001302296700001902309700001602328856004902344       2019                        Engldsh    a0006-349500aSpectral Assignment of Lysozyme Collective Vibrations0 aSpectral Assignment of Lysozyme Collective Vibrations  cFeb  a564A-564A0 v1163 a<div class="section-paragraph">Global structural vibrations at terahertz (THz) frequencies have been associated with protein function and allosteric control. A chief obstacle to utilizing this control mechanism has been measurement of specific motions. Recently it was shown that while the vibrational density of states, and isotropic absorption spectra are broad and featureless, collective vibrations can be isolated based on their directionality using aligned samples (realized with protein crystals) and anisotropic THz microscopy [1]. However the assignment of resonant bands to specific structural motions was complicated by the high symmetry of the tetragonal crystals used, and the slow experimental method. To structurally map the vibrations of the chicken egg white lysozyme (CEWL) we measure anisotropic absorption of triclinic crystals using our new technique: ideal polarization varying anisotropic THz microscopy (IPV-ATM). The low symmetry triclinic crystals provide absolute protein orientation, and the near field IPV-ATM rapidly measures broadband terahertz linear dichroism of the microcrystals. All measurements were performed at room temperature under 100% humidity conditions. The unit cell parameters of triclinic lysozyme nitrate crystals, α = 28.5A°, b = 32.7A°, c = 35.1A°, α = 88.2°, β = 108.9°, γ = 111.9°, belonging to the P1 space group, were determined by X-ray diffraction before and after THz measurements. The intramolecular vibrational absorbance of the triclinic crystals has a more complex polarization dependence than the higher symmetry tetragonal crystals, as expected. While the tetragonal crystals have two strong bands at 45cm<sup>−1</sup> and 55cm<sup>−1</sup>, the triclinic crystals have a series of narrow bands between 40 and 60cm<sup>−1</sup> and a prominent band at 30cm<sup>−1</sup>. We compare the measured spectra to normal mode ensemble averaged calculations to assign the observed resonances, and isolating which collective motions impact the catalytic site.</div>10aBiophysics1 aDeng, Y., T.1 aMcKinney, J.1 aRomo, T.1 aGrossfield, A.1 aMarkelz, A.  uhttps://markelz.physics.buffalo.edu/node/249