Two-step binding mechanism for T-cell receptor recognition of peptide MHC

T cells probe a diverse milieu of peptides presented by molecules of the major histocompatibility complex (MHC) by using the T-cell receptor (TCR) to scan these ligands with high sensitivity and specificity. Here we describe a physical basis for this scanning process by studying the residues involved in both the initial association and the stable binding of TCR to peptide-MHC, using the well-characterized TCR and peptide-MHC pair of 2B4 and MCC-IE(k) (moth cytochrome c, residues 88 103). We show that MHC contacts dictate the initial association, guiding TCR docking in a way that is mainly independent of the peptide. Subsequently, MCC-IE(k) peptide contacts dominate stabilization, imparting specificity and influencing T-cell activation by modulating the duration of binding. This functional subdivision of the peptide-MHC ligand suggests that a two-step process for TCR recognition facilitates the efficient scanning of diverse peptide-MHC complexes on the surface of cells and also makes TCRs inherently crossreactive towards different peptides bound by the same MHC.     

Ordered porous materials for emerging applications

"Space--the final frontier." This preamble to a well-known television series captures the challenge encountered not only in space travel adventures, but also in the field of porous materials, which aims to control the size, shape and uniformity of the porous space and the atoms and molecules that define it. The past decade has seen significant advances in the ability to fabricate new porous solids with ordered structures from a wide range of different materials. This has resulted in materials with unusual properties and broadened their application range beyond the traditional use as catalysts and adsorbents. In fact, porous materials now seem set to contribute to developments in areas ranging from microelectronics to medical diagnosis.     

Recent mass balance of polar ice sheets inferred from patterns of global sea-level change

Global sea level is an indicator of climate change, as it is sensitive to both thermal expansion of the oceans and a reduction of land-based glaciers. Global sea-level rise has been estimated by correcting observations from tide gauges for glacial isostatic adjustment--the continuing sea-level response due to melting of Late Pleistocene ice--and by computing the global mean of these residual trends. In such analyses, spatial patterns of sea-level rise are assumed to be signals that will average out over geographically distributed tide-gauge data. But a long history of modelling studies has demonstrated that non-uniform--that is, non-eustatic--sea-level redistributions can be produced by variations in the volume of the polar ice sheets. Here we present numerical predictions of gravitationally consistent patterns of sea-level change following variations in either the Antarctic or Greenland ice sheets or the melting of a suite of small mountain glaciers. These predictions are characterized by geometrically distinct patterns that reconcile spatial variations in previously published sea-level records. Under the--albeit coarse--assumption of a globally uniform thermal expansion of the oceans, our approach suggests melting of the Greenland ice complex over the last century equivalent to -0.6 mm yr(-1) of sea-level rise.     

Genome sequence of Yersinia pestis, the causative agent of plague

The Gram-negative bacterium Yersinia pestis is the causative agent of the systemic invasive infectious disease classically referred to as plague, and has been responsible for three human pandemics: the Justinian plague (sixth to eighth centuries), the Black Death (fourteenth to nineteenth centuries) and modern plague (nineteenth century to the present day). The recent identification of strains resistant to multiple drugs and the potential use of Y. pestis as an agent of biological warfare mean that plague still poses a threat to human health. Here we report the complete genome sequence of Y. pestis strain CO92, consisting of a 4.65-megabase (Mb) chromosome and three plasmids of 96.2 kilobases (kb), 70.3 kb and 9.6 kb. The genome is unusually rich in insertion sequences and displays anomalies in GC base-composition bias, indicating frequent intragenomic recombination. Many genes seem to have been acquired from other bacteria and viruses (including adhesins, secretion systems and insecticidal toxins). The genome contains around 150 pseudogenes, many of which are remnants of a redundant enteropathogenic lifestyle. The evidence of ongoing genome fluidity, expansion and decay suggests Y. pestis is a pathogen that has undergone large-scale genetic flux and provides a unique insight into the ways in which new and highly virulent pathogens evolve.     

呼肠孤病毒科斐济病毒属一新种: 南方水稻黑条矮缩病毒

近年在广东省和海南省部分地区新发生一种水稻病毒病, 其症状表现为植株矮缩、叶色深绿、叶背及茎秆出现条状乳白色或深褐色小突起、高位分蘖及茎节部倒生气生须根. 病株韧皮部细胞内可观察到具斐济病毒特征性晶格状排列直径为70~75 nm的球状病毒粒体以及病毒基质和管状结构. 从发病田块及其附近的玉米(Zea mays)、稗草(Echinochloa crusgalli)、水莎草(Juncellus serotinus)和白草(Pennisetum flaccidum)植株体内检测到病原病毒的存在. 田间调查及室内传毒实验表明, 白背飞虱(Sogatella furcifera)是该病毒的主要传毒介体. 该病毒的基因组由10条dsRNA组成, 其电泳图谱与水稻黑条矮缩病毒(Rice black-streaked dwarf virus)基本相同. 采用接头单引物扩增法获得了该病毒基因组两个片段(S9和S10)全长核苷酸序列, 两者在核苷酸组成、末端序列及基因排列上均具斐济病毒特征, 但与斐济病毒属已知种核苷酸同一率小于75% (S9)和80% (S10), 基于核苷酸及其推导编码产物氨基酸序列构建的系统进化树表明, 该病毒在斐济病毒属中处于相对独立的进化位置. 结果表明, 该病毒应为呼肠孤病毒科(Reoviridae)斐济病毒属(Fijivirus)第2组的一个新种, 建议将其命名为南方水稻黑条矮缩病毒(Southern rice black-streaked dwarf virus).     

谈原真性（Authenticity）

>authenticity是当前国际文化遗产领域中一个特别重要的术语,它出现在众多国际文化遗产文献当中,在文化遗产价值认证和文化遗产保护实践中起着不可替代的作用。国际遗产界的重要文件《奈良文献》即指出：“原真性……看来是评审遗产价值的本质因素。对原真性的认识,在所有的文化遗产研究中,在保护与修复规划中,在《世界遗产公约》和其他文化遗产目录所采用的申报程序中,发挥着基础性作用。”因此,准确理解和翻译这个术语,对于中国遗产界具有重要的理论和实践意义。然而,目前国内对于authenticity的翻译仍然处于混乱状态,多种译法并存。在各种译法中,尤以将其译为“真实性”最为常见。该译法散见于各类学术研究中,并见诸官方文件,如2004年2月15日国务院办公厅转发了九个部委联合发布的《关于加强我国世界文化遗产保护管理工作的意见》。这个文件中使用的就是“真实性”提法。那么将authenticity一词译为“真实性”是否合适呢？下面从该词本身的意义着手,进行细致分析。authenticity一词起源于中世纪的欧洲,在希腊语和拉丁语中有“权威的”(authoritative)和“原初的”(original)含义。它并非是文化遗产领域的专用术语,早在现代文化遗产理论出现之前,就已应用于伦理学、语言学、文学艺术等领域。在宗教占统治力量的中世纪,authenticity用来指宗教经本及宗教遗物的真实性^[1]。在英文词典Webster’s 9th New Collegiate Dictionary的释义中,authenticity有original(原初的)、real(真实的)、trustworthy(可信的)三层含义。英国文化遗产专家David Lowenthal认为,authenticity表示与“虚假”(false)相对应的“真正”(true),与“伪造”(fake)相对应的“真实”(real),与“复制”(copy)相对应的“原作”(original),与“欺骗”(corrupt)相对应的“诚实”(honest),与“世俗”(profane)相对应的“神圣”(sacred)。^[1]当“authenticity”一词应用于文化遗产领域时,是指文化遗产本身和所有相关信息的“原初”“真实”和“可信”。如果将authenticity译为“真实性”,此种翻译只表达了其中的real(真实的)、trustworthy(可信的)两层含义,而original(原初的)这层含义,却没有体现出来。但这层含义对于遗产理论和实践有着不可忽略的意义。original(原初的),包含着时间维度上的“真”,其中original可理解为第一手的,非复制的。这层意思表明,authenticity中的“真”,是一个与时间相关的概念,即时间起点和整个时间序列上各个点对于起始状态的“真”的反映。举个简单的例子,当面对一只在今天制造的金手镯时,人们讨论其是否是“真”,一般是指其是否用纯金制成;而面对一只古代的金手镯,当讨论其是否是“真”,不仅指其材料,更是指向时间维度,即这只金手镯是否是制造于古代而不是现代;如果这是一只古代著名人物用过的金手镯,那这个“真”还指代特定历史年代和特定历史人物,而这些信息都是不能复制的,都是“原”的。所以,“原”和“真”在指向的内容上有一定的交集,但并不是完全重合。在文化遗产领域翻译authenticity时,“原”的含义是不可以省略的。不恰当的翻译容易导致意思的缺损,会造成对术语的片面理解,影响人们对文化遗产领域中一些重要问题的判断,给文化遗产保护实践带来负面影响。一些学者提出了更为恰当的译法,其中“原真性”就是其中之一。张松提出：“原真性(authenticity),又译原生性、真实性、确实性、可靠性,主要有原始的、原创的、第一手的、非复制、非仿造等意思。”^[2]张成渝^[3],阮仪三^[4-5]等人都在文章中直接使用“原真性”作为“authenticity”一词的翻译。与其他译法相比,“原真性”一词中的“原”与“original”这层含义对应,“真”与“real”和“trustworthy”对应,完整得表达出了“authenticity”中所包含的三重含义,弥补了原译法的不足。这种译法能够与多样的文化遗产相适应,是对“authenticity”较为确切的中文翻译。