Control of respiration by nitric oxide in Keilin-Hartree particles,mitochondria and SH-SY5Y neuroblastoma cells

The pattern of cytochrome c oxidase inhibition by nitric oxide (NO) was investigated polarographically using Keilin-Hartree particles, mitochondria and human neuroblastoma cells. NO reacts with purified cytochrome c oxidase forming either a nitrosyl- or a nitrite-inhibited derivative, displaying distinct kinetics and light sensitivity of respiration recovery in the absence of free NO. Keilin-Hartree particles or cells, respiring either on endogenous substrates alone or in the presence of ascorbate, as well as state 3and state 4mitochondria respiring on glutamate and malate, displayed the rapid recovery characteristic of the nitrite derivative. All systems, when respiring in the presence of tetramethyl-p-phenylenediamine, were characterised by the slower, light-sensitive recovery typical of the nitrosyl derivative. Together the results suggest that the reaction of NO with cytochrome c oxidase in situ follows two alternative inhibition pathways, depending on the electron flux through the respiratory chain.Received 1 April 2003; received after revision 22 May 2003; accepted 3 June 2003     

Selection and evolution of enzymes from a partially randomized non-catalytic scaffold

Enzymes are exceptional catalysts that facilitate a wide variety of reactions under mild conditions, achieving high rate-enhancements with excellent chemo-, regio- and stereoselectivities. There is considerable interest in developing new enzymes for the synthesis of chemicals and pharmaceuticals and as tools for molecular biology. Methods have been developed for modifying and improving existing enzymes through screening, selection and directed evolution. However, the design and evolution of truly novel enzymes has relied on extensive knowledge of the mechanism of the reaction. Here we show that genuinely new enzymatic activities can be created de novo without the need for prior mechanistic information by selection from a naive protein library of very high diversity, with product formation as the sole selection criterion. We used messenger RNA display, in which proteins are covalently linked to their encoding mRNA, to select for functional proteins from an in vitro translated protein library of >10(12 )independent sequences without the constraints imposed by any in vivo step. This technique has been used to evolve new peptides and proteins that can bind a specific ligand, from both random-sequence libraries and libraries based on a known protein fold. We now describe the isolation of novel RNA ligases from a library that is based on a zinc finger scaffold, followed by in vitro directed evolution to further optimize these enzymes. The resulting ligases exhibit multiple turnover with rate enhancements of more than two-million-fold.     

ESCRT-III recognition by VPS4 ATPases

The ESCRT (endosomal sorting complex required for transport) pathway is required for terminal membrane fission events in several important biological processes, including endosomal intraluminal vesicle formation, HIV budding and cytokinesis. VPS4 ATPases perform a key function in this pathway by recognizing membrane-associated ESCRT-III assemblies and catalysing their disassembly, possibly in conjunction with membrane fission. Here we show that the microtubule interacting and transport (MIT) domains of human VPS4A and VPS4B bind conserved sequence motifs located at the carboxy termini of the CHMP1-3 class of ESCRT-III proteins. Structures of VPS4A MIT-CHMP1A and VPS4B MIT-CHMP2B complexes reveal that the C-terminal CHMP motif forms an amphipathic helix that binds in a groove between the last two helices of the tetratricopeptide-like repeat (TPR) of the VPS4 MIT domain, but in the opposite orientation to that of a canonical TPR interaction. Distinct pockets in the MIT domain bind three conserved leucine residues of the CHMP motif, and mutations that inhibit these interactions block VPS4 recruitment, impair endosomal protein sorting and relieve dominant-negative VPS4 inhibition of HIV budding. Thus, our studies reveal how the VPS4 ATPases recognize their CHMP substrates to facilitate the membrane fission events required for the release of viruses, endosomal vesicles and daughter cells.     

Transferrin receptor 1 is a cellular receptor for New World haemorrhagic fever arenaviruses

At least five arenaviruses cause viral haemorrhagic fevers in humans. Lassa virus, an Old World arenavirus, uses the cellular receptor alpha-dystroglycan to infect cells. Machupo, Guanarito, Junin and Sabia viruses are New World haemorrhagic fever viruses that do not use alpha-dystroglycan. Here we show a specific, high-affinity association between transferrin receptor 1 (TfR1) and the entry glycoprotein (GP) of Machupo virus. Expression of human TfR1, but not human transferrin receptor 2, in hamster cell lines markedly enhanced the infection of viruses pseudotyped with the GP of Machupo, Guanarito and Junin viruses, but not with those of Lassa or lymphocytic choriomeningitis viruses. An anti-TfR1 antibody efficiently inhibited the replication of Machupo, Guanarito, Junin and Sabia viruses, but not that of Lassa virus. Iron depletion of culture medium enhanced, and iron supplementation decreased, the efficiency of infection by Junin and Machupo but not Lassa pseudoviruses. These data indicate that TfR1 is a cellular receptor for New World haemorrhagic fever arenaviruses.     

基于OpenSEES的剪力墙低周往复荷载试验的数值分析

框支剪力墙结构的广州花园酒店,原结构及改造后结构均不满足我国现行规范的抗震构造要求,为了了解改造前后结构的剪力墙抗震性能,本文作者对不同配筋与构造的剪力墙进行了低周往复荷试验,同时采用多竖向弹簧单元（MVLEM）,通过二次开发编制了基于OpenSEES的剪力墙结构分析程序SWNA,通过SWNA对剪力墙结构进行低周往复试验数值模拟,结果表明该数值方法能够较很好地从宏观上模拟剪力墙弹塑性行为,包括中和轴移动,剪切变形影响、局部塑性状态及破坏机制等。MVLEM单元可以通过比较少的自由度模拟剪力墙结构,节省大量计算时间,适用于高层建筑结构的整体弹塑性分析及基于性能的抗震评定。 关键词:剪力墙 低周往复荷载试验 OpenSEES MVLEM 弹塑性分析     

Forecasting time‐varying covariance with a robust Bayesian threshold model

This paper proposes a robust multivariate threshold vector autoregressive model with generalized autoregressive conditional heteroskedasticities and dynamic conditional correlations to describe conditional mean, volatility and correlation asymmetries in financial markets. In addition, the threshold variable for regime switching is formulated as a weighted average of endogenous variables to eliminate excessively subjective belief in the threshold variable decision and to serve as the proxy in deciding which market should be the price leader. The estimation is performed using Markov chain Monte Carlo methods. Furthermore, several meaningful criteria are introduced to assess the forecasting performance in the conditional covariance matrix. The proposed methodology is illustrated using daily S&P500 futures and spot prices. Copyright © 2010 John Wiley & Sons, Ltd.