A short synthesis of highly soluble chemoselective chitosan derivatives via "click chemistry"

A short synthesis of chemoselective chitosan derivatives was achieved by copper-catalyzed Huisgen cycloaddition, which is an ideal reaction for click chemistry, by using N-(4-azidophthaloyl)-chitosan. N-(4-azidophthaloyl)-chitosan was prepared through chemoselective N-bromophthaloylation of chitosan in acidic water and subsequent azidation. The obtained N-(4-bromopthaloyl)-chitosan had higher solubility in common solvents than conventional phthaloyl chitosan. N-(4-azidophthaloyl)-chitosan was successfully converted with ethynyl derivatives having functional groups (hydroxymethyl, phenyl, and methyl ester) in the presence of copper(II) sulfate, sodium ascorbate and/or trimethylamine. FT-IR spectra, elemental analyses, and (1)H and (13)C NMR spectra supported that the desired chitosan derivatives were chemoselectively transferred by these groups with a 1,4-triazole linker.     

Structure of the chloroplast NADH dehydrogenase-like complex: nomenclature for nuclear-encoded subunits

The chloroplast NADH dehydrogenase-like complex (NDH) was first discovered based on its similarity to complex I in respiratory electron transport, and is involved in electron transport from photoproduced stromal reductants such as NADPH and ferredoxin to the intersystem plastoqunone pool. However, a recent study suggested that it is a ferredoxin-dependent plastoquinone reductase rather than an NAD(P)H dehydrogenase. Furthermore, recent advances in subunit analysis of NDH have revealed the presence of a novel hydrophilic subcomplex on the stromal side of the thylakoid membrane, as well as an unexpected lumenal subcomplex. This review discusses these new studies on the structure of NDH, and proposes a unified nomenclature for newly discovered NDH subunits.     

Inhibition of PSII in atrazine-tolerant tobacco cells by barbatic acid, a lichen-derived depside

In atrazine-tolerant tobacco cells with Ser to Thr mutation at the 264th amino acid of PsbA polypeptide in photosystem II (PSII), electron trannsport around the secondary quinone acceptor (Q(B)) site was inhibited to a greater extent by barbatic acid than in wild-type cells. Further characterization suggests similar mode of action of barbatic acid and phenyl-type herbicides.     

Structure, function, and evolution of the PsbP protein family in higher plants

The PsbP is a thylakoid lumenal subunit of photosystem II (PSII), which has developed specifically in higher plants and green algae. In higher plants, the molecular function of PsbP has been intensively investigated by release-reconstitution experiments in vitro. Recently, solution of a high-resolution structure of PsbP has enabled investigation of structure-function relationships, and efficient gene-silencing techniques have demonstrated the crucial role of PsbP in PSII activity in vivo. Furthermore, genomic and proteomic studies have shown that PsbP belongs to the divergent PsbP protein family, which consists of about 10 members in model plants such as Arabidopsis and rice. Characterization of the molecular function of PsbP homologs using Arabidopsis mutants suggests that each plays a distinct and important function in maintaining photosynthetic electron transfer. In this review, recent findings regarding the molecular functions of PsbP and other PsbP homologs in higher plants are summarized, and the molecular evolution of these proteins is discussed.     

Responses of the chloroplast glyoxalase system to high CO2 concentrations

ABSTRACT

Sugar metabolism pathways such as photosynthesis produce dicarbonyls, e.g. methylglyoxal (MG), which can cause cellular damage. The glyoxalase (GLX) system comprises two enzymes GLX1 and GLX2, and detoxifies MG; however, this system is poorly understood in the chloroplast, compared with the cytosol. In the present study, we determined GLX1 and GLX2 activities in spinach chloroplasts, which constituted 40% and 10%, respectively, of the total leaf glyoxalase activity. In Arabidopsis thaliana, five GFP-fusion GLXs were present in the chloroplasts. Under high CO₂ concentrations, where increased photosynthesis promotes the MG production, GLX1 and GLX2 activities in A. thaliana increased and the expression of AtGLX1-2 and AtGLX2-5 was enhanced. On the basis of these findings and the phylogeny of GLX in oxygenic phototrophs, we propose that the GLX system scavenges MG produced in chloroplasts during photosynthesis.     

Preparation and characterization of monolayer and multilayer Langmuir-Blodgett films of a series of 6-O-alkylcelluloses

Monolayer and multilayer Langmuir-Blodgett (LB) films of 6-O-alkylcelluloses with various chain lengths were prepared and studied. The surface pressure (pi)-area (A) isotherms of 6-O-alkylcelluloses exhibited characteristic behaviors depending on the length of the alkyl chain and temperature. 6-O-Stearylcellulose on the subphase formed a homogeneous monolayer at 10 mN m(-1). By transfer ratio, FT-IR, and contact angle measurements, it was proved that the monolayer of 6-O-stearylcellulose on the water surface was transferred successfully onto a substrate by a vertical dipping method to form a Z-type LB film. The transmission and reflection absorption IR spectrum indicated that the hydrocarbon chains had all-trans rotamers and were oriented nearly perpendicular to the surface in the film. AFM section analysis revealed that the thickness per layer was calculated to be 2.35 nm. These results suggested that the hydrocarbon chains were inclined at an angle of about 25.3 degrees to have high packing density in the alkyl region.     

Functional analysis of four members of the PsbP family in photosystem II in Nicotiana tabacum using differential RNA interference

Gene redundancy is frequently found in higher plants and complicates genetic analysis. In this study, a method referred to as 'differential RNA interference (dRNAi)' was used to investigate the psbP gene family in Nicotiana tabacum. PsbP is a membrane-extrinsic subunit of PSII and plays important roles in the water splitting reaction. N. tabacum has four psbP isogenes and the function of each isogene has not yet been characterized in vivo. To obtain transgenic tobacco plants with various amounts and compositions of PsbP members, the psbP isogenes were differentially silenced by RNA interference (RNAi) using the 3'-untranslated region (UTR) as a silencing trigger (dRNAi). In addition, the extra psbP genes without the 3'-UTR were complementarily transformed into the above silenced plants, which accumulated PsbP originating from the exogenous gene while differential silencing of the endogenous target was maintained. By using dRNAi and subsequent complementation (substitution) in dRNAi, we clearly demonstrated that, regardless of the of PsbP members that were accumulated, PSII activity was linearly correlated with the total amount of PsbP. Therefore, we concluded that the protein functions of the PsbP members in N. tabacum are equivalent in vivo, whereas full expression of the four isogenes is required for optimum PSII activity. These results demonstrate that the use of dRNAi and subsequent complementation/substitution in dRNAi would provide a new experimental approach for studying the function of multigene families in plants.     

A truncated mutant of the extrinsic 23-kDa protein that absolutely requires the extrinsic 17-kDa protein for Ca2+ retention in photosystem II

One function of the extrinsic 23-kDa protein in photosystem II (OEC23) is to retain Ca(2+ )and Cl(-), two essential cofactors for photosynthetic oxygen evolution. A truncated mutant of OEC23 (OEC23 Delta19) revealed that 19 residues of the N-terminus of OEC23 were necessary for Ca(2+ )retention but not for its proper interaction with OEC17, the extrinsic 17-kDa protein in photosystem II. The lost ability of OEC23 Delta19 to reconstitute the oxygen-evolving activity was partially restored by OEC17 binding, suggesting the involvement of OEC17 in Ca(2+ )retention in photosystem II.     

A region corresponding to second aspartate-rich motif in tryptophan isoprenylating enzyme,ComQ, serves as a substrate-binding site

Posttranslational isoprenylation of a tryptophan residue identified from Bacillus quorum sensing pheromone, ComX pheromone, is unique and essential for the bioactivity. A modifying enzyme, ComQ, forms ComX pheromone from the ComX precursor and isoprenyl pyrophosphate and exhibits moderate similarity to isoprenyl pyrophosphate synthases. We investigated non-conserved region in ComQ, corresponding to isopentenyl pyrophosphate binding region of the synthases, using in vitro cell-free isoprenylation. These results suggested that the only conserved aspartic acid residue in the region of ComQ is critical for enzyme activity and responsible for ComX binding. Our findings should contribute to basic understanding of the mechanism of tryptophan isoprenylation.