Energy Landscape and Dynamics of Biomolecules Extended Abstract

Proteins are not isolated homogeneous systems. Each protein can exist in a very large number of conformations (conformational substates) that are characterized by an energy landscape. The main conformational motions, similar to the α and β fluctuations in glasses, are linked to fluctuations in the bulk solvent and the hydration shell.     

Emulsion stabilizing properties of various chitosans in the presence of whey protein isolate

The emulsion stabilizing potential of chitosans (CN) with various molecular weights and degrees of deacetylation (CNI=1494 kDa, 78.1%DD; CNHI=694 kDa, 78.5%DD; CNHI2=319 kDa, 78.5%DD; CNHK=749 kDa, 67.7%DD) was compared in the presence of whey protein isolate. Phase separation evolutions revealed minimal stabilizing concentrations against syneresis from 0.1 to 0.125% in most CN preparations, except CNHI2 where it was higher (0.225%). Those stabilizing concentrations are the result of interfacial coadsorption saturation of CN with proteins, favouring interfacial electrostatic and steric stabilizing mechanisms. The emulsion characteristics (droplet size, limiting low-shear viscosity, and surface net charge), mostly distinctive at 0.1%CN, revealed the following order of stabilizing potentials: CNI≈CNHI>CNHK>CNHI2, which is in agreement with respective phase separation evolutions. The lower stabilizing potential of CNHI2 is explained by lower interfacial coadsorption efficiency with protein. In spite of a higher interfacial load of CNHK vs. CNI and CNHI, its lower stabilizing potential is essentially explained by a lower surface net charge.     

异三聚体G蛋白在NAA诱导的拟南芥根生长发育中的作用

以拟南芥的野生型(ws)、异三聚体G蛋白α亚基基因GPA1缺失突变体(gpa1-1,gpa1-2)和超表达突变体(wGα,cGα)为材料,通过施加不同浓度(0~0.2 mg/L)的NAA处理,对拟南芥根生长发育的一些形态指标进行了观测比较.结果表明:(1)随着培养基中NAA浓度的不断升高,5种基因型主根的伸长生长均受到抑制,且抑制作用随浓度升高而增强;4种突变体和野生型主根的生长在相同浓度NAA处理下,无明显差异;(2)NAA在一定浓度范围内,对拟南芥侧根的生长发育起促进作用;在NAA诱导的侧根生长中,G蛋白超表达突变体比野生型更敏感,缺失突变体则不敏感.初步证明G蛋白不参与主根生长发育的调节,而在侧根生长发育中可能起正调节作用.     

Optimal Length Transportation Hypothesis to Model Proteasome Product Size Distribution

This paper discusses translocation features of the 20S proteasome in order to explain typical proteasome length distributions. We assume that the protein transport depends significantly on the fragment length with some optimal length which is transported most efficiently. By means of a simple one-channel model, we show that this hypothesis can explain both the one- and the three-peak length distributions found in experiments. A possible mechanism of such translocation is provided by so-called fluctuation-driven transport.     

Protein Turnover in Response to Transient Exposure to Exogenous Auxin is Necessary for Restoring Auxin Autotrophy in a Stressed Arachis hypogea Cell Culture

An auxin autotrophic Arachis hypogea cell culture was sensitive to stress treatments leading to water loss whereas the growth of its auxin-supplemented counterpart was unaffected under similar conditions. Here we show that an hour of transient auxin treatment in the post stress period was sufficient for restoring the auxin autotrophic growth potential of the stress driven quiescent Arachis cells. Qualitative proteome analysis revealed protein turnover to have a role in mediating auxin-originated signals in these cells. In consonance, MG132 a cell permeable inhibitor of the ubiquitin mediated protein turnover completely inhibited the auxin dependent growth restoration of the stressed Arachis cells. Thus protein turnover is a necessary downstream event in exogenous auxin mediated stress tolerance in Arachis cells.     

The first crystal structure of class III superoxide reductase from Treponema pallidum

Superoxide reductase (SOR) is a metalloprotein containing a non-heme iron centre, responsible for the scavenging of superoxide radicals in the cell. The crystal structure of Treponema pallidum (Tp) SOR was determined using soft X-rays and synchrotron radiation. Crystals of the oxidized form were obtained using poly(ethylene glycol) and MgCl₂ and diffracted beyond 1.55 Å resolution. The overall architecture is very similar to that of other known SORs but TpSOR contains an N-terminal domain in which the desulforedoxin-type Fe centre, found in other SORs, is absent. This domain conserves the β-barrel topology with an overall arrangement very similar to that of other SOR proteins where the centre is present. The absence of the iron ion and its ligands, however, causes a decrease in the cohesion of the domain and some disorder is observed, particularly in the region where the metal would be harboured. The C-terminal domain exhibits the characteristic immunoglobulin-like fold and harbours the Fe(His)₄(Cys) active site. The five ligands of the iron centre are well conserved despite some disorder observed for one of the four molecules in the asymmetric unit. The participation of a glutamate as the sixth ligand of some of the iron centres in Pyrococcus furiosus SOR was not observed in TpSOR. A possible explanation is that either X-ray photoreduction occurred or there was a mixture of redox states at the start of data collection. In agreement with earlier proposals, details in the TpSOR structure also suggest that Lys49 might be involved in attraction of superoxide to the active site.This work is dedicated to the memory of Prof. Frank Rusnak.Coordinates and observed structure factor amplitudes have been deposited in the Protein Data Bank under the accession code 1Y07.