Comparison of the effects of Triton X-100 treatment on the protein secondary structure of Photosystem I and Photosystem II studied by FT-IR spectroscopy

Photocatalytic photosystem I/PEDOT composite films prepared by vapor-phase polymerization

Photosystem I (PSI) achieves photo-induced charge separation with outstanding internal quantum efficiency and has been used to improve the performance of various photoelectrochemical systems. Herein, we describe a fast and versatile technique to assemble composite films containing PSI and a chosen intrinsically conductive polymer (ICP). A mixture of PSI and a Friedel-Crafts catalyst (FeCl₃) is drop cast atop a substrate of choice. Contact with ICP monomer vapor at low temperature stimulates polymer growth throughout PSI films in minutes. We assess the effects of PSI loading on the rapid vapor-phase growth of poly(3,4-ethylenedioxythiophene) (PEDOT) within and above PSI multilayer films, and characterize the resulting film's thickness, electrochemical capacitance, and photocatalytic response. Composite films generate cathodic photocurrent when in contact with an aqueous redox electrolyte, confirming retention of the photocatalytic activity of the polymer-entrapped PSI multilayer assembly.

Characterization of the structural changes and photochemical activity of photosystem I under Al(3+) effect

The photochemical activity of photosystem I (PSI) as affected by Al(3+) was investigated in thylakoid membranes and PSI submembrane fractions isolated from spinach. Biophysical and biochemical techniques such as oxygen uptake, light induced absorbance changes at 820nm, chlorophyll fluorescence emission, SDS-polyacrylamide gel electrophoresis, and FTIR spectroscopy have been used to analyze the sites and action modes of this cation on the PSI complex. Our results showed that Al(3+) above 3mM induces changes in the redox state of P700 reflected by an increase of P700 photooxidation phase and a delay of the slower rate of P700 re-reduction which reveals that Al(3+) exerted an inhibitory action at the donor side of PSI especially at plastocyanin (PC). Furthermore, results of P700 photooxidation monitored in the presence of DCMU with or without MV suggested that the same range of Al(3+) concentrations impairs the photochemical reaction centers (RC) of PSI, as shown by the decline in the amount of active population of P700, and disrupts the charge separation between P700 and the primary electron acceptor A0 leading to the inhibition of electron transfer at the acceptor side of PSI. These inhibitory actions were also accompanied by an impairment of the energy transfer from light harvesting complex (LHCI) to RC of PSI, following the disconnection of LHCI antenna as illustrated by an enhancement of chlorophyll fluorescence emission spectra at low temperature (77K). The above results coincided with FTIR measurements that indicated a conformational change of the protein secondary structures in PSI complex where 25% of α-helix was converted into β-sheet, β-antiparallel and turn structures. These structural changes in PSI complex proteins are closely related with the alteration photochemical activity of PSI including the inhibition of the electron transport through both acceptor and donor sides of PSI.

Discrimination of cultivation ages and cultivars of ginseng leaves using Fourier transform infrared spectroscopy combined with multivariate analysis

To determine whether Fourier transform (FT)-IR spectral analysis combined with multivariate analysis of whole-cell extracts from ginseng leaves can be applied as a high-throughput discrimination system of cultivation ages and cultivars, a total of total 480 leaf samples belonging to 12 categories corresponding to four different cultivars (Yunpung, Kumpung, Chunpung, and an open-pollinated variety) and three different cultivation ages (1 yr, 2 yr, and 3 yr) were subjected to FT-IR. The spectral data were analyzed by principal component analysis and partial least squares-discriminant analysis. A dendrogram based on hierarchical clustering analysis of the FT-IR spectral data on ginseng leaves showed that leaf samples were initially segregated into three groups in a cultivation age-dependent manner. Then, within the same cultivation age group, leaf samples were clustered into four subgroups in a cultivar-dependent manner. The overall prediction accuracy for discrimination of cultivars and cultivation ages was 94.8% in a cross-validation test. These results clearly show that the FT-IR spectra combined with multivariate analysis from ginseng leaves can be applied as an alternative tool for discriminating of ginseng cultivars and cultivation ages. Therefore, we suggest that this result could be used as a rapid and reliable F1 hybrid seed-screening tool for accelerating the conventional breeding of ginseng.

Characterization of photosystem I from spinach: effect of solution pH

Our previous work has demonstrated the isolation of photosystem I (PSI) from spinach using ultrafiltration with a final purity of 84%. In order to get a higher purity of PSI and more importantly to develop a practical bioseparation process, key physiochemical properties of PSI and their dependence on operational parameters must be assessed. In this study, the effect of solution pH, one of the most important operating parameters for membrane process, on the property of PSI was examined. Following the isolation of crude PSI from spinach using n-dodecyl-beta-D: -maltoside as detergent, the isoelectric point, aggregation size, zeta potential, low-temperature fluorescence, atomic force microscopy imaging, secondary structure, and thermal stability were determined. Solution pH was found to have a significant effect on the activity, aggregation size and thermal stability of PSI. The results also suggested that the activity of PSI was related to its aggregation size.

Entrapment of photosystem I within self-assembled films

We have developed a process to incorporate an integral membrane protein, Photosystem I (PSI), into an organic thin film at an electrode surface and thereby insulate the protein complex on the surface while mimicking its natural environment. The PSI complex, which is primarily more hydrophobic on the exterior than interior, is hydrophobically confined in vivo within the thylakoid membrane. To mimic the thylakoid membrane and entrap PSI on an electrode, we have designed a series of steps using a thin self-assembled monolayer (SAM) to adsorb and orient PSI followed by exposures to longer-chained methyl-terminated alkanethiols that place exchange with components of the original SAM in the interprotein domains. In this process, PSI is first adsorbed onto a HOC(6)S/Au substrate through a short exposure to a dilute solution of the protein to achieve a protein coverage of approximately 25%. The PSI/HOC(6)S/Au substrate is then placed into a solution containing one of various longer-chained alkanethiols including C(22)SH or C(18)OC(19)SH. Changes in thickness, interfacial capacitance, infrared spectra, and surface wettability were used to assess the extent of backfilling by the long-chained thiols. The coverage of the protein layer and the solvent used for backfilling affected the rate and quality of the SAM formed in the interprotein regions. After exposure of the PSI layer to solvents containing alkanethiols, there was only minor loss of protein on the surface and no real change in protein secondary structure as evidenced by reflectance absorption infrared spectroscopy.

The studies of FT-IR and CD spectroscopy on catechol oxidase I from tobacco

A novel copper-containing enzyme named COI (catechol oxidase I) has been isolated and purified from tobacco by extracting acetone-emerged powder with phosphate buffer, centrifugation at low temperature, ammonium sulfate fractional precipitation, and column chromatography on DEAE-sephadex (A-50), sephadex (G-75), and DEAE-celluse (DE-52). PAGE, SDS-PAGE were used to detect the enzyme purity, and to determine its molecular weight. Then the secondary structures of COI at different pH, different temperatures and different concentrations of guanidine hydrochloride (GdnHCl) were studied by the FT-IR, Fourier self-deconvolution spectra, and circular dichroism (CD). At pH 2.0, the contents of both alpha-helix and anti-parallel beta-sheet decrease, and that of random coil increases, while beta-turn is unchanged compared with the neutral condition (pH 7.0). At pH 11.0, the results indicate that the contents of alpha-helix, anti-parallel beta-sheet and beta-turn decrease, while random coil structure increases. According to the CD measurements, the relative average fractions of alpha-helix, anti-parallel beta-sheet, beta-turn/parallel beta-sheet, aromatic residues and disulfide bond, and random coil/gamma-turn are 41.7%, 16.7%, 23.5%, 11.3%, and 6.8% at pH 7.0, respectively, while 7.2%, 7.7%, 15.2%, 10.7%, 59.2% at pH 2.0, and 20.6%, 9.5%, 15.2%, 10.5%, 44.2% at pH 11.0. Both alpha-helix and random coil decrease with temperature increasing, and anti-parallel beta-sheet increases at the same time. After incubated in 6 mol/L guanidine hydrochloride for 30 min, the fraction of alpha-helix almost disappears (only 1.1% left), while random coil/gamma-turn increases to 81.8%, which coincides well with the results obtained through enzymatic activity experiment.

Molecular reorganization induced by Ca2+ of plant photosystem I reconstituted into phosphatidylglycerol liposomes

The interaction of divalent cations with biomembranes is important for a number of biological processes. In this study, the regulatory effect of Ca2+ on the interaction between plant spinach photosystem I (PSI) particles and negatively charged lipid phosphatidylglycerol (PG) was investigated by circular dichroism (CD) spectroscopy. It was found that in the absence of CaCl2, PG causes an increase in alpha-helix and a decrease in disordered conformations of protein secondary structures of PSI, the beta-sheet and turns being almost unaffected. Meanwhile, the same effect also enhances the excitonic interactions relating to Chl a and Chl b from the PSI core complex and external antenna light-harvesting complex (LHCI). By contrast, in the presence of CaCl2, PG hardly interferes with the structure of the proteins' skeleton of PSI, but it can depress the excitonic interactions for Chl b of LHCI and for PSI core complex Chl a at (-) 433.5 nm of the CD signal which is accompanied by a blue shift of its peak. It is most likely that the neutralization of the phosphate groups in the PSI-PG complex and the negative surface charges of PSI, and partial dehydration in the vicinity of the ester CO region of the PG polar head group by the Ca-ions modify the interaction between PSI and PG, thereby inducing molecular reorganization of protein and pigments within both the external antenna LHCI and PSI core complex in proteoliposomes.

Effect of phosphatidylglycerol on molecular organization of photosystem I

Phosphatidylglycerol (PG) is the only anionic phospholipid in photosynthetic membrane. In this study, photosystem I (PSI) particles obtained from plant spinach were reconstituted into PG liposomes at a relatively high concentration. The results from visible absorption, fluorescence emission, and circular dichroism (CD) spectra reveal an existence of the interactions of PSI with PG. PG effect causes blue-shift and intensity decrease of Chl a peak bands in the absorption and 77 K fluorescence emission. The visible CD spectra indicate that the excitonic interactions for Chl a and Chl b molecules were enhanced upon reconstitution. Furthermore, more or less blue- or red-shift of the peaks characterized by Chl a, Chl b, and carotenoid molecules are also occurred. Simultaneously, an increase in alpha-helix and a decrease particularly in the disordered conformations of protein secondary structures are observed. In addition, the same effect also leads to somewhat more tryptophan (Trp) residues exposed to the polar environment. These results demonstrate that some alteration of molecular organization occurs within both the external antenna LHCI and PSI core complex after PSI reconstitution.

Self-regulation phenomena applied to bacterial reaction centers: 2. Nonequilibrium adiabatic potential: dark and light conformations revisited

Experimental and theoretical results in support of nonlinear dynamic behavior of photosynthetic reaction centers under light-activated conditions are presented. Different conditions of light adaptation allow for preparation of reaction centers in either of two different conformational states. These states were detected both by short actinic flashes and by the switching of the actinic illumination level between different stationary state values. In the second method, the equilibration kinetics of reaction centers isolated from Rhodobacter sphaeroides were shown to be inherently biphasic. The fast and slow equilibration kinetics are shown to correspond to electron transfer (charge separation) at a fixed structure and to combined electron-conformational transitions governed by the bounded diffusion along the potential surface, respectively. The primary donor recovery kinetics after an actinic flash revealed a pronounced dependence on the time interval (deltat) between cessation of a lengthy preillumination of a sample and the actinic flash. A pronounced slow relaxation component with a decay half time of more than 50 s was measured for deltat > 10 s. This component corresponds to charge recombination in reaction centers for which light-induced structural changes have not relaxed completely before the flash. The amplitude of this component depended on the conditions of the sample preparation, specifically on the type of detergent used in the preparation. The redox potential parameters as well as the structural diffusion constants were estimated for samples prepared in different ways.

Involvement of active oxygen species in degradation of light-harvesting proteins under light stresses

This paper presents evidence for light-mediated degradation of isolated light-harvesting proteins (Lhc2) and involvement of oxygen free radicals in the process. The time course of light harvesting photodestruction is much slower than that of D1 protein (requiring hours for complete breakdown). By use of mass spectrometry and amino acid sequencing, it has been revealed that the primary cleavages take place in the hydrophilic portion of the NH(2) region where oxygen-containing radicals attack randomly and not at specific sites. Moreover, these chlorophyll binding proteins are completely fragmented. From the effectiveness of scavengers and the preliminary electron paramagnetic resonance measurements reported, it appears that singlet oxygen is involved as a short-lived species, and hydroxyl and alkoxyl radicals act at higher light intensity or over a longer time, whereas hydrogen peroxide and superoxide anions are not observed. Antenna proteins appear more resistance to photodestruction in their monomeric form than in trimeric form, while minor antenna are highly sensitive. However, the organization of both minor and major proteins in the photosystem II supracomplex affords some photoprotection. Interestingly, leaves exposed to strong light contained degraded major antenna, unlike those kept in the dark, which is consistent with studies on the illumination of isolated proteins, supporting the hypothesis that active oxygen species play a role in vivo in the short-term acclimative adaptation of plants.

Phosphatidylcholine-induced reactivation of photosystem II membranes pretreated with Triton X-100

Triton X-100-induced inactivation and phosphatidylcholine-induced reactivation of photosystem II (PSII) membranes were investigated using oxygen electrode, variable fluorescence and spectroscopic techniques including absorption and circular dichroism spectroscopy. Incubation of the PSII membrane with Triton X-100 reduced the oxygen-evolving rate, modified the variable chlorophyll fluorescence kinetics, changed the protein secondary structures, altered the chlorophyll binding state to proteins and decreased the excitonic interaction of chlorophyll molecules. Phosphatidylcholine addition did not change the protein secondary structures, but could partially reactivate the reduced oxygen-evolving rate, and partly reversed the variable fluorescence parameters, the chlorophyll binding state and the excitonic interaction of the chlorophyll molecules. The results indicate that the phosphatidylcholine environment can optimize the tertiary structures of PSII.