Parameters of the Protein Energy Landscapes of Several Light-Harvesting Complexes Probed via Spectral Hole Growth Kinetics Measurements

44 Pag., 2 Tabl. The definitive version is available at: http://pubs.acs.org/journal/jpcbfkThe parameters of barrier distributions on the protein energy landscape in the excited electronic state of the pigment/protein system have been determined by means of spectral hole burning for the lowest-energy pigments of CP43 core antenna complex and CP29 minor antenna complex of spinach Photosystem II (PS II) as well as of trimeric and monomeric LHCII complexes transiently associated with the pea Photosystem I (PS I) pool. All of these complexes exhibit sixty to several hundred times lower spectral hole burning yields as compared with molecular glassy solids previously probed by means of the hole growth kinetics measurements. Therefore, the entities (groups of atoms), which participate in conformational changes in protein, appear to be significantly larger and heavier than those in molecular glasses. No evidence of a small (1 cm−1) spectral shift tier of the spectral diffusion dynamics has been observed. Therefore, our data most likely reflect the true barrier distributions of the intact protein and not those related to the interface or surrounding host. Possible applications of the barrier distributions as well as the assignments of low-energy states of CP29 and LHCII are discussed in light of the above results.Research at Concordia University is supported by NSERC and CFI. R.P. would like to thank Spanish MICINN (grant AGL2008-00377). M.S. acknowledges the contribution of the Photosynthetic Systems Program, Chemical Sciences, Geosciences, and Biosciences Division, Basic Energy Sciences, USDOE. J.P. and K.-D.I. gratefully acknowledge support from Deutsche Forschungsgemeinschaft (SFB 429, TP A1, and TP A3, respectively).Peer reviewe

Two-photon excited fluorescence from higher electronic states of chlorophylls in photosynthetic antenna complexes: a new approach to detect strong excitonic chlorophyll a/b coupling.

Stepwise two-photon excitation of chlorophyll a and b in the higher plant main light-harvesting complex (LHC II) and the minor complex CP29 (as well as in organic solution) with 100-fs pulses in the Q(y) region results in a weak blue fluorescence. The dependence of the spectral shape of the blue fluorescence on excitation wavelength offers a new approach to elucidate the long-standing problem of the origin of spectral "chlorophyll forms" in pigment-protein complexes, in particular the characterization of chlorophyll a/b-heterodimers. As a first result we present evidence for the existence of strong chlorophyll a/b-interactions (excitonically coupled transitions at 650 and 680 nm) in LHC II at ambient temperature. In comparison with LHC II, the experiments with CP29 provide further evidence that the lowest energy chlorophyll a transition (at approximately 680 nm) is not excitonically coupled to chlorophyll b

Vibrational dynamics of plant light-harvesting complex LHC II investigated by quasi- and inelastic neutron scattering

Vibrational dynamics of the light-harvesting complex II (LHC II) from spinach was investigated by quasi- and inelastic neutron scattering (QENS and INS) at three different temperatures of 80, 160, and 285 K. QENS/INS spectra of solubilised LHC II and of the corresponding buffer solution were obtained separately and exhibit characteristic inelastic features. After subtraction of the buffer contribution, the INS spectrum of LHC II reveals a distinct Boson peak at ∼ 2.5 meV at 80 K that shifts towards lower energies if the temperature is increased to 285 K. This effect is interpreted in terms of a “softening” of the protein matrix along with the dynamical transition at ∼ 240 K. Our findings indicate that INS is a valuable method to obtain the density of vibrational states not only at cryogenic, but also at physiological temperatures

Vibrational dynamics of plant light-harvesting complex LHC II investigated by quasi- and inelastic neutron scattering

Vibrational dynamics of the light-harvesting complex II (LHC II) from spinach was investigated by quasi- and inelastic neutron scattering (QENS and INS) at three different temperatures of 80, 160, and 285 K. QENS/INS spectra of solubilised LHC II and of the corresponding buffer solution were obtained separately and exhibit characteristic inelastic features. After subtraction of the buffer contribution, the INS spectrum of LHC II reveals a distinct Boson peak at ∼ 2.5 meV at 80 K that shifts towards lower energies if the temperature is increased to 285 K. This effect is interpreted in terms of a “softening” of the protein matrix along with the dynamical transition at ∼ 240 K. Our findings indicate that INS is a valuable method to obtain the density of vibrational states not only at cryogenic, but also at physiological temperatures

Parameters of the Protein Energy Landscapes of Several Light-Harvesting Complexes Probed via Spectral Hole Growth Kinetics Measurements

44 Pag., 2 Tabl. The definitive version is available at: http://pubs.acs.org/journal/jpcbfkThe parameters of barrier distributions on the protein energy landscape in the excited electronic state of the pigment/protein system have been determined by means of spectral hole burning for the lowest-energy pigments of CP43 core antenna complex and CP29 minor antenna complex of spinach Photosystem II (PS II) as well as of trimeric and monomeric LHCII complexes transiently associated with the pea Photosystem I (PS I) pool. All of these complexes exhibit sixty to several hundred times lower spectral hole burning yields as compared with molecular glassy solids previously probed by means of the hole growth kinetics measurements. Therefore, the entities (groups of atoms), which participate in conformational changes in protein, appear to be significantly larger and heavier than those in molecular glasses. No evidence of a small (1 cm−1) spectral shift tier of the spectral diffusion dynamics has been observed. Therefore, our data most likely reflect the true barrier distributions of the intact protein and not those related to the interface or surrounding host. Possible applications of the barrier distributions as well as the assignments of low-energy states of CP29 and LHCII are discussed in light of the above results.Research at Concordia University is supported by NSERC and CFI. R.P. would like to thank Spanish MICINN (grant AGL2008-00377). M.S. acknowledges the contribution of the Photosynthetic Systems Program, Chemical Sciences, Geosciences, and Biosciences Division, Basic Energy Sciences, USDOE. J.P. and K.-D.I. gratefully acknowledge support from Deutsche Forschungsgemeinschaft (SFB 429, TP A1, and TP A3, respectively).Peer reviewe