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The plant hormone jasmonate plays crucial roles in regulating plant responses to herbivorous insects and microbial pathogens and is an important regulator of plant growth and development. Key mediators of jasmonate signalling include MYC transcription factors, which are repressed by jasmonate ZIM-domain (JAZ) transcriptional repressors in the resting state. In the presence of active jasmonate, JAZ proteins function as jasmonate co-receptors by forming a hormone-dependent complex with COI1, the F-box subunit of an SCF-type ubiquitin E3 ligase. The hormone-dependent formation of the COI1-JAZ co-receptor complex leads to ubiquitination and proteasome-dependent degradation of JAZ repressors and release of MYC proteins from transcriptional repression. The mechanism by which JAZ proteins repress MYC transcription factors and how JAZ proteins switch between the repressor function in the absence of hormone and the co-receptor function in the presence of hormone remain enigmatic. Here we show that Arabidopsis MYC3 undergoes pronounced conformational changes when bound to the conserved Jas motif of the JAZ9 repressor. The Jas motif, previously shown to bind to hormone as a partly unwound helix, forms a complete α-helix that displaces the amino (N)-terminal helix of MYC3 and becomes an integral part of the MYC N-terminal fold. In this position, the Jas helix competitively inhibits MYC3 interaction with the MED25 subunit of the transcriptional Mediator complex. Our structural and functional studies elucidate a dynamic molecular switch mechanism that governs the repression and activation of a major plant hormone pathway. [ABSTRACT FROM AUTHOR]

Examines the functional role of the amino terminal cytoplasmic domain of mammalian A-type potassium channel. Conformation of the amino terminal of cytoplasmic domain of Shaker channel; Changes in channel properties by the deletion of different domains in amino terminal; Changes in single channel current amplitude; Involvement of the terminal in ion permeation process.

In this work, selenylation of Artemisia sphaerocephala polysaccharide (SeASP MW ) was studied by using H 2 SeO 3 /HNO 3 /BaCl 2 reaction system in microwave field. SeASP MW exhibited the Se content range of 111–264 μg/g with high yields (72.1–94.9%). 13 C NMR results indicated that the weak C-6 substitution was occurred. The decrease (from 7.348 × 10 4 g/mol to 1.736–4.667 × 10 4 g/mol) in weight average molecular mass ( M W ) of SeASP MW was observed in size exclusion chromatography combined with multi angle laser light scattering (SEC-MALLS) analysis. SeASP MW exhibited a more rigid solution conformation which might be due to the degradation of polysaccharide chains in acidic reaction reagent. This was also supported by atomic force microscopy (AFM) result that SeASP MW showed short chains and island-like topography. In anti-tumor activity assays, SeASP MW6 exhibited the inhibition rates of 32.381% and 39.776% against human non-small cell lung cancer cell line (H1650) at the concentration of 100 and 200 μg/mL, respectively. The relatively weak inhibition effect of SeASP MW was not related to cell apoptosis and cell cycle arrest, suggesting Se content might be a key factor to influence the anti-tumor activities of selenized polysaccharides in vitro . [ABSTRACT FROM AUTHOR]

Abstract: Sulfated polysaccharides exerted potent biological property which was relative to degree of sulfation (DS), M w, substitution position and chain conformation. In the present study, sulfated derivatives of Artemisia sphaerocephala polysaccharide (ASP) with different DS were synthesized by chlorosulfuric acid/pyridine method. FT-IR and 13C NMR analysis indicated that C-6 substitution was predominant in sulfated ASP (SASP) compared with other positions at C-2. In the sulfation reaction, a sharp decrease in M w was observed in SASP. The d f values from 1.96 to 2.77 indicated that the –SO3H groups leading to the relatively expanded conformation of SASP. Antioxidant assays showed that SASP had better antioxidant activities. The data obtained in vitro models indicated that high DS and moderate M w showed the best antioxidant capacities. [Copyright &y& Elsevier]

Abstract: The conventional extraction methods for polysaccharides were time-consuming, laborious and energy-consuming. Microwave-assisted extraction (MAE) technique was employed for the extraction of Artemisia sphaerocephala polysaccharides (ASP), which is a traditional Chinese food. The extracting parameters were optimized by Box-Behnken design. In microwave heating process, a decrease in molecular weight (M w) was detected in SEC-LLS measurement. A d f value of 2.85 indicated ASP using MAE exhibited as a sphere conformation of branched clusters in aqueous solution. Furthermore, it showed stronger antioxidant activities compared with hot water extraction. The data obtained showed that the molecular weights played a more important role in antioxidant activities. [Copyright &y& Elsevier]