Structure and Interactions of the Chlorophyll a Molecules in the Higher Plant Lhcb4 Antenna Protein

Temperature-Caused Changes in Raman Pattern and Protein Profiles of Winter Triticale (x Triticosecale, Wittm.) Field-Grown Seedlings

Climate change, which causes periods with relatively high temperatures in winter in Poland, can lead to a shortening or interruption of the cold hardening of crops. Previous research indicates that cold acclimation is of key importance in the process of acquiring cereal tolerance to stress factors. The objective of this work was to verify the hypothesis that both natural temperature fluctuations and the plant genotype influence the content of metabolites as well as proteins, including antioxidant enzymes and photosystem proteins. The research material involved four winter triticale genotypes, differing in their tolerance to stress under controlled conditions. The values of chlorophyll a fluorescence parameters and antioxidant activity were measured in their seedlings. Subsequently, the contribution of selected proteins was verified using specific antibodies. In parallel, the profiling of the contents of chlorophylls, carotenoids, phenolic compounds, and proteins was carried out by Raman spectroscopy. The obtained results indicate that a better PSII performance along with a higher photosystem II proteins content and thioredoxin reductase abundance were accompanied by a higher antioxidant activity in the field-grown triticale seedlings. The Raman studies showed that the cold hardening led to a variation in photosynthetic dyes and an increase in the phenolic to carotenoids ratio in all DH lines.

Macroscale Light-Controlled Lubrication Enabled by Introducing Diarylethene Molecules in a Nanoconfinement

Reversible friction regulation is of long-standing great interest in the fields of both industry and scientific research, so some materials and theories have been developed aiming to solve this problem. Light-sensitive materials are promising because of the easy controllable switching of the properties and structures. Here, a reversible light-controlled macrolubrication was realized by regulating the performance of nanoscale light-sensitive molecules adsorbed on contact surfaces. In this work, symmetric diarylethene and asymmetric diarylethene had been designed and synthesized as functional materials. The friction forces were found to be obviously increased upon exposure to ultraviolet light and decayed to the initial value under visible light. In addition, the friction coefficient changed alternately with ultraviolet and visible illumination. According to the results of experiments and simulation of material properties, the behavior was suggested to be attributed to the difference in shear stiffness of the nanoscale diarylethene molecule adsorption layer triggered by two wavelength lights. This work not only provides a new lubrication regulation technology but also develops intelligent engineering materials.

Tuning antenna function through hydrogen bonds to chlorophyll a

We describe a molecular mechanism tuning the functional properties of chlorophyll a (Chl-a) molecules in photosynthetic antenna proteins. Light-harvesting complexes from photosystem II in higher plants - specifically LHCII purified with α- or β-dodecyl-maltoside, along with CP29 - were probed by low-temperature absorption and resonance Raman spectroscopies. We show that hydrogen bonding to the conjugated keto carbonyl group of protein-bound Chl-a tunes the energy of its Soret and Q_y absorption transitions, inducing red-shifts that are proportional to the strength of the hydrogen bond involved. Chls-a with non-H-bonded keto C13¹ groups exhibit the blue-most absorption bands, while both transitions are progressively red-shifted with increasing hydrogen-bonding strength - by up 382 & 605 cm^-1 in the Q_y and Soret band, respectively. These hydrogen bonds thus tune the site energy of Chl-a in light-harvesting proteins, determining (at least in part) the cascade of energy transfer events in these complexes.

Surface-enhanced Raman scattering spectra revealing the inter-cultivar differences for Chinese ornamental Flos Chrysanthemum: a new promising method for plant taxonomy

BACKGROUND

Flos Chrysanthemi, as a part of Chinese culture for a long history, is valuable for not only environmental decoration but also the medicine and food additive. Due to their voluminously various breeds and extensive distributions worldwide, it is burdensome to make recognition and classification among numerous cultivars with conventional methods which still rest on the level of morphologic observation and description. As a fingerprint spectrum for parsing molecular information, surface-enhanced Raman scattering (SERS) could be a suitable candidate technique to characterize and distinguish the inter-cultivar differences at molecular level.

RESULTS

SERS spectra were used to analyze the inter-cultivar differences among 26 cultivars of Chinese ornamental Flos Chrysanthemum. The characteristic peaks distribution patterns were abstracted from SERS spectra and varied from cultivars to cultivars. For the bands distributed in the pattern map, the similarities in general showed their commonality while in the finer scales, the deviations and especially the particular bands owned by few cultivars revealed their individualities. Since the Raman peaks could characterize specific chemical components, those diversity of patterns could indicate the inter-cultivar differences at the chemical level in fact.

CONCLUSION

In this paper, SERS technique is feasible for distinguishing the inter-cultivar differences among Flos Chrysanthemum. The Raman spectral library was built with SERS characteristic peak distribution patterns. A new method was proposed for Flos Chrysanthemum recognition and taxonomy.

Vibrational techniques applied to photosynthesis: Resonance Raman and fluorescence line-narrowing

Resonance Raman spectroscopy may yield precise information on the conformation of, and the interactions assumed by, the chromophores involved in the first steps of the photosynthetic process. Selectivity is achieved via resonance with the absorption transition of the chromophore of interest. Fluorescence line-narrowing spectroscopy is a complementary technique, in that it provides the same level of information (structure, conformation, interactions), but in this case for the emitting pigment(s) only (whether isolated or in an ensemble of interacting chromophores). The selectivity provided by these vibrational techniques allows for the analysis of pigment molecules not only when they are isolated in solvents, but also when embedded in soluble or membrane proteins and even, as shown recently, in vivo. They can be used, for instance, to relate the electronic properties of these pigment molecules to their structure and/or the physical properties of their environment. These techniques are even able to follow subtle changes in chromophore conformation associated with regulatory processes. After a short introduction to the physical principles that govern resonance Raman and fluorescence line-narrowing spectroscopies, the information content of the vibrational spectra of chlorophyll and carotenoid molecules is described in this article, together with the experiments which helped in determining which structural parameter(s) each vibrational band is sensitive to. A selection of applications is then presented, in order to illustrate how these techniques have been used in the field of photosynthesis, and what type of information has been obtained. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems.

Spectral modulation observed in Chl-a by ultrafast laser spectroscopy

Broadband real-time dynamic vibronic coupling in Chl-a were experimentally studied using few cycle laser pulses of 6.8fs duration and a 128-channnel lock-in amplifier. Thanks to the extreme temporal resolution benefitting from the ultrashort laser pulse, the real-time modulation of the electronic transition energy induced by the molecular vibrations were calculated by the time dependent first moments of the bleaching band. The transition energy was found to be modulated periodically with the same frequencies of molecular vibration found in the Fourier amplitude spectrum of the difference absorbance real-time traces. This was interpreted to be due to the difference in the effective transition energy associated with the wavepacket motion induced by the equilibrium positions of potential curves between the ground state and the excited state. Using the values, Huang-Rhys factors for several vibrational modes involved in the spectral modulation at the room-temperature have been determined.

Real-time vibrational dynamics in chlorophyll a studied with a few-cycle pulse laser

We use a 6.8-fs laser as the light source for broad-band femtosecond pump-probe real-time vibrational spectroscopy to investigate both electronic relaxation and vibrational dynamics of the Q(y)-band of Chl-a at 293 K. More than 25 vibrational modes coupled to the Q(y) transition are observed. Eleven of them have been clarified predominantly due to the excited state, and six of them are concluded to be nearly exclusively resulting from the ground-state wave-packet motion. Moreover, thanks to the broad-band detection over 5000 cm⁻¹, the modulated signals due to the excited state vibrational coherence are observed on both sides of the 0-0 transition with equal separation. The corresponding nonlinear process has been studied using a three-level model, from which the probe wavelength dependence of the phase of the periodic modulation can be calculated. The probe wavelength dependence of the vibrational amplitude is interpreted in terms of the interaction between the "pump" or "laser," Stokes, and anti-Stokes field intermediated by the molecular vibrations. In addition, an excited state absorption peak at ~709 nm has been observed. To the best of our knowledge, this is the first study of broad-band real-time vibrational spectroscopy in Chl-a.

Raman properties of chlorophyll d, the major pigment of Acaryochloris marina: studies using both Raman spectroscopy and density functional theory

The Raman spectroscopy of purified chlorophyll (Chl) d extracted from Acaryochloris marina has been measured over the wide region of 250-3200 cm(-1) at 77 K following excitation of its Soret band at 488 nm and analyzed with the aid of hybrid density-functional vibrational analyses. A Raman peak specific to Chl d, which arises from the formyl group 3(1) C=O stretching, was clearly observed at 1659 cm(-1) with medium intensity. Peaks due to other C=O stretching vibrations of the 13(1) keto-, 13(3) ester- and 17(3) groups were also observed. Four very strong peaks were observed in the range of 1000-1600 cm(-1), assigned to the CC stretching and mixtures of the CH3 bend and CN stretching. CCC and NCC bending contribute to medium intensity peaks at 986 and 915 cm(-1). Out-of-plane CH bending at Chl d methine sites 10, 5 and 20 contribute to observed peaks at 885, 864 and 853 cm(-1), respectively. A few modes involving the MgN stretching and MgNC bending motions were observed in the very low frequency range. Density functional theory (DFT) calculations have been used to make assignments on the observed Raman spectrum and the DFT results have been found to be in good agreement with the experimental results.

A structural investigation of the central chlorophyll a binding sites in the minor photosystem II antenna protein, Lhcb4

Mutant proteins from light-harvesting complexes of higher plants may be obtained by expressing modified apoproteins in Escherichia coli, and reconstituting them in the presence of chlorophyll and carotenoid cofactors. This method has allowed, in particular, the engineering of mutant LHCs in which each of the residues coordinating the central Mg atoms of the chlorophylls was replaced by noncoordinating amino acids [Bassi, R., Croce, R., Cugini, D., and Sandonà, D. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 10056-10061]. The availability of these mutants is of particular importance for determining the precise position of absorption bands for the different chlorophyll molecules, as well as the sequence of energy transfer events that occur within LHC complexes, provided that the structural impact of each mutation is precisely evaluated. Using resonance Raman spectroscopy, we have characterized the pigment-protein interactions in the minor photosystem II antenna protein, Lhcb4 (CP29), in which each of three of the four central chlorophyll a molecules has been removed by such mutations. By comparing the spectra of these mutants with those of the wild-type protein, the state of interaction of the carbonyl group, the coordination state of the central magnesium ion, and the dielectric constant (polarity) of the immediate environment in the binding pocket of the chlorophyll a molecule were defined for each cofactor binding site. In addition, the structural impact of the absence of one chlorophyll a molecule and the quality of protein folding were evaluated for each of these mutated polypeptides.

Probing the binding sites of exchanged chlorophyll a in LH2 by Raman and site-selection fluorescence spectroscopies

In this work we have selectively released the 800 nm absorbing bacteriochlorophyll a molecules of the LH2 protein from the photosynthetic bacterium Rhodopseudomonas acidophila, strain 10050, and replaced them with chlorophyll a (Chla). A combination of low-temperature electronic absorption, resonance Raman and site-selection fluorescence spectroscopies revealed that the Chla pigments are indeed bound in the B800 binding site; this is the first work that formally proves that such non-native chlorins can be inserted correctly into LH2.