Density of Vibrational States of the Light-Harvesting Complex II of Green Plants Studied by Inelastic Neutron Scattering

Abstract

Results of inelastic neutron scattering (INS) experiments are reported for the solubilized trimeric light-harvesting complex of photosystem II (LHC II) in the temperature range from 5 to 100 K. Two incident neutron wavelengths of 2.0 (∼20 meV) and 5.1 Å (∼3.2 meV) corresponding to elastic energy resolutions of ∆E ) 0.920 meV and ∆E ) 0.093 meV, respectively, are employed to study INS spectra of LHC II for both neutron energy loss and gain. Solubilized LHC II and D 2 O-containing buffer solution are investigated separately in order to properly subtract the contribution of the solvent. The inelastic part of the scattering function S(Q,ω) derived for the LHC II protein resembles the well-known "Boson-peak" and is characterized by a maximum at about 2.5 meV and a strongly asymmetric line shape with a slight tailing toward higher energy transfers. Analysis of the momentum transfer dependence of S(Q,ω) reveals that both the elastic and inelastic contributions to S(Q,ω) exhibit the characteristics of vibrational protein motions. Furthermore, the effective density of vibrational states is derived from the experimental data. Finally, the data are discussed in comparison to recent results of line-narrowing optical spectroscopies et al. J. Phys. Chem. B 2001, 105, 7115). The wide distribution of vibrational frequencies found for LHC II is interpreted in terms of structurally inequivalent protein domains within the LHC II trimer leading to a partial localization of protein phonons.

The functional role of protein dynamics in photosynthetic reaction centers investigated by elastic and quasielastic neutron scattering

“…6 (red points) and compared to the average atomic mean square displacements < u 2 > of PS II membrane fragments equilibrated at different hydration levels [10,13]. The INS spectra exhibit a distinct Boson peak at ∼ 7.5 meV at 20 K, which shifts to 2.5 meV at 250 K. This observation differs from the low-temperature 02013-p.3 behavior of the antenna complex LHC II, where the vibrational density of states was found to be widely similar up to 100 K [30,31]. In contrast, the shift of the Boson peak in the case of PS II membrane fragments indicates a softening of the protein matrix along with the onset of molecular dynamics.…”

Protein and solvent dynamics of the water-soluble chlorophyll-binding protein (WSCP)

“…As a complicating factor for such studies, a significant solvent contribution to the overall scattering intensity can be expected as observed before for the antenna complex LHC II [15] and for the bacterial reaction center [16,17]. In the present study we address this problem by QENS experiments on WSCP and on the corresponding buffer solution at room temperature.…”

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

“…Furthermore, H 2 O contained in the buffer solution was replaced by D 2 O following the method described in [10] in order to reduce the scattering contribution of the solvent. The LHC II content in the solubilized sample was determined independently to be about 300 mg in a total volume of 2 ml according to the procedure described in [10].…”

“…Furthermore, H 2 O contained in the buffer solution was replaced by D 2 O following the method described in [10] in order to reduce the scattering contribution of the solvent. The LHC II content in the solubilized sample was determined independently to be about 300 mg in a total volume of 2 ml according to the procedure described in [10]. Furthermore, it was checked by extensive EPJ Web of Conferences biochemical analyses prior to and after the neutron scattering experiment that the sample remained intact in its native trimeric form [10] preventing aggregation [11] and monomerization [12].…”

“…which was kept constant for all temperatures assuming a small variation of u 2 [10] and ii) the temperature prefactor that can be described as [13] …”