ABA is a major phytohormone that regulates a broad range of plant traits and is especially important for adaptation to environmental conditions. Our understanding of the molecular basis of ABA ...responses in plants improved dramatically in 2009 and 2010, banner years for ABA research. There are three major components; PYR/PYL/ RCAR (an ABA receptor), type 2C protein phosphatase (PP2C; a negative regulator) and SNF1-related protein kinase 2 (SnRK2; a positive regulator), and they offer a double negative regulatory system, PYR/PYL/RCAR--| PP2C--| SnRK2. In the absence of ABA, PP2C inactivates SnRK2 by direct dephosphorylation. In response to environmental or developmental cues, ABA promotes the interaction of PYR/PYL/RCAR and PP2C, resulting in PP2C inhibition and SnRK2 activation. This signaling complex can work in both the nucleus and cytosol, as it has been shown that SnRK2 phosphorylates basic-domain leucine zipper (bZIP) transcription factors or membrane proteins. Several structural analyses of PYR/PYL/RCAR have provided the mechanistic basis for this 'core signaling' model, by elucidating the mechanism of ABA binding of receptors, or the 'gate-latch-lock' mechanism of interaction with PP2C in inhibiting activity. On the other hand, intercellular ABA transport had remained a major issue, as had intracellular ABA signaling. Recently, two plasma membrane-type ABC transporters were identified and shed light on the influx/efflux system of ABA, resolving how ABA is transported from cell to cell in plants. Our knowledge of ABA responses in plants has been greatly expanded from intracellular signaling to intercellular transport of ABA.
Mutations in mitochondrial DNA (mtDNA) accumulate in tissues of mammalian species and have been hypothesized to contribute to aging. We show that mice expressing a proofreading-deficient version of ...the mitochondrial DNA polymerase g (POLG) accumulate mtDNA mutations and display features of accelerated aging. Accumulation of mtDNA mutations was not associated with increased markers of oxidative stress or a defect in cellular proliferation, but was correlated with the induction of apoptotic markers, particularly in tissues characterized by rapid cellular turnover. The levels of apoptotic markers were also found to increase during aging in normal mice. Thus, accumulation of mtDNA mutations that promote apoptosis may be a central mechanism driving mammalian aging.
Autism spectrum disorder (ASD) is a neurodevelopmental disorder with an unknown molecular pathogenesis. A recent molecular focus has been the mutated neuroligin 3, neuroligin 3(R451C), in ...gain-of-function studies and for its role in induced impairment of synaptic function, but endoplasmic reticulum (ER) stress induced by mutated molecules also deserves investigation. We previously found two missense mutations, H246N and Y251S, in the gene-encoding synaptic cell adhesion molecule-1 (CADM1) in ASD patients, including cleavage of the mutated CADM1 and its intracellular accumulation. In this study, we found that the mutated CADM1 showed slightly reduced homophilic interactions in vitro but that most of its interactions persist. The mutated CADM1 also showed morphological abnormalities, including shorter dendrites, and impaired synaptogenesis in neurons. Wild-type CADM1 was partly localized to the ER of C2C5 cells, whereas mutated CADM1 mainly accumulated in the ER despite different sensitivities toward 4-phenyl butyric acid with chemical chaperone activity and rapamycin with promotion activity for degradation of the aggregated protein. Modeling analysis suggested a direct relationship between the mutations and the conformation alteration. Both mutated CADM1 and neuroligin 3(R451C) induced upregulation of C/EBP-homologous protein (CHOP), an ER stress marker, suggesting that in addition to the trafficking impairment, this CHOP upregulation may also be involved in ASD pathogenesis.
In order to study catechin compositions in five Japanese persimmons: Hiratanenashi (HN), Tone-wase (TW), Ishibashi-wase (IW), Maekawa-jiro (MJ) and Matsumoto-wase-fuyu (MF), the contents of ...epigallocatechin (EGC), catechin (C), and epicatechin (EC) were determined. Total phenolic contents were also determined for the studies of the catechin composition. Identification and quantification of the catechins were performed by HPLC. The EGC contents in three astringent persimmons (HN, TW and IW) were higher than those of two non-astringent persimmons (MJ and MF). The EGC content in HN (astringent) was the highest among the five Japanese persimmons. The EGC content in MF (non-astringent) was the lowest among the five Japanese persimmons. Therefore, astringent persimmons may be better sources of the natural antioxidant, EGC, than non-astringent persimmons, and HN (astringent) may be the best source of EGC among the five Japanese persimmons. This is the first comparative study of catechin compositions in five Japanese persimmons.
The three-dimensional structure of oryzacystatin-I, a cysteine proteinase inhibitor of the rice, Oryza sativa L. japonica, has been determined in solution at pH 6.8 and 25 °C by 1H and 15N NMR ...spectroscopy. The main body (Glu13−Asp97) of oryzacystatin-I is well-defined and consists of an α-helix and a five-stranded antiparallel β-sheet, while the N- and C-terminal regions (Ser2−Val12 and Ala98−Ala102) are less defined. The helix-sheet architechture of oryzacystatin-I is stabilized by a hydrophobic cluster formed between the α-helix and the β-sheet and is considerably similar to that of monellin, a sweet-tasting protein from an African berry, as well as those of the animal cystatins studied, e.g., chicken egg white cystatin and human stefins A and B (also referred to as human cystatins A and B). Detailed structural comparison indicates that oryzacystatin-I is more similar to chicken cystatin, which belongs to the type-2 animal cystatins, than to human stefins A and B, which belong to the type-1 animal cystatins, despite different loop length.
Carboxylate (COO−) groups can coordinate to metal ions in of the following four modes: ‘unidentate’, ‘bidentate’, ‘bridging’ and ‘pseudo-bridging’ modes. COO− stretching frequencies provide ...information about the coordination modes of COO− groups to metal ions. We review the Fourier-transform infrared spectroscopy (FTIR) of side-chain COO− groups of Ca2+-binding proteins: pike parvalbumin pI 4.10, bovine calmodulin and Akazara scallop troponin C. FTIR spectroscopy of Akazara scallop troponin C has demonstrated that the coordination structure of Mg2+ is distinctly different from that of Ca2+ in the Ca2+-binding site. The assignments of the COO− antisymmetric stretch have been ensured on the basis of the spectra of calcium-binding peptide analogues. The downshift of the COO− antisymmetric stretching mode from 1565 cm-1 to 1555–1540 cm−1 upon Ca2+ binding is a commonly observed feature of FTIR spectra for EF-hand proteins.
It is possible to travel back in time at the molecular level by reconstructing proteins from extinct organisms. Here we report the reconstruction, based on sequence predicted by phylogenetic ...analysis, of seven Precambrian thioredoxin enzymes (Trx) dating back between ~1.4 and ~4 billion years (Gyr). The reconstructed enzymes are up to 32 °C more stable than modern enzymes, and the oldest show markedly higher activity than extant ones at pH 5. We probed the mechanisms of reduction of these enzymes using single-molecule force spectroscopy. From the force dependency of the rate of reduction of an engineered substrate, we conclude that ancient Trxs use chemical mechanisms of reduction similar to those of modern enzymes. Although Trx enzymes have maintained their reductase chemistry unchanged, they have adapted over 4 Gyr to the changes in temperature and ocean acidity that characterize the evolution of the global environment from ancient to modern Earth.
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