Multiple diverse ligands binding at a single protein site: A matter of pre-existing populations

Here, we comment on the steadily increasing body of data showing that proteins with specificity actually bind ligands of diverse shapes, sizes, and composition. Such a phenomenon is not surprising when one considers that binding is a dynamic process with populations in equilibrium and that the shape of the binding site is strongly influenced by the molecular partner. It derives implicitly from the concept of populations. All proteins, specific and nonspecific, exist in ensembles of substates. If the library of ligands in solution is large enough, favorably matching ligands with altered shapes and sizes can be expected to bind, with a redistribution of the protein populations. Point mutations at spatially distant sites may exert large conformational rearrangements and hinge effects, consistent with mutations away from the binding site leading to population shifts and (cross-)drug resistance. A similar effect is observed in protein superfamilies, in which different sequences with similar topologies display similar large-scale dynamic motions. The hinges are frequently at analogous sites, yet with different substrate specificity. Similar topologies yield similar conformational isomers, although with different distributions of population times, owing to the change in the conditions, that is, the change in the sequences. In turn, different distributions relate to binding of different sizes and shapes. Hence, the binding site shape and size are defined by the ligand. They are not independent entities of fixed proportions and cannot be analyzed independently of the binding partner. Such a proposition derives from viewing proteins as dynamic distributions, presenting to the incoming ligands a range of binding site shapes. It illustrates how presumably specific binding molecules can bind multiple ligands. In terms of drug design, the ability of a single receptor to recognize many dissimilar ligands shows the need to consider more diverse molecules. It provides a rationale for higher affinity inhibitors that are not derived from substrates at their transition states and indicates flexible docking schemes.     

同一山洞中五种蝙蝠的回声定位比较及生态位的分化

对同一山洞中5种蝙蝠的回声定位叫声和外部形态作了比较分析,根据蝙蝠回声定位叫声,形态特征与捕食策略之间的联系,并结合部分的野外观察研究,推断其捕食生境及捕食策略,并对洞中5种共栖蝙蝠的生态位分化进行了分析;研究结果如下：（1）南蝠（Ia io)在地面或树冠中间的开阔空间捕食个体较大的昆虫;（2）大鼠耳蝠（Myotis myotis)主要以掠食性方式（gleaning) 捕食森林或草地地表面的昆虫;（3）黄大蹄幅（Hipposideros pratti)主要在树冠周围或树冠上方进行捕蝇器式（Fly-catching)（即倒挂于一固定枝条或地点,探索周围飞行或接近的昆虫,探索到后捕捉回原倒挂地点再进食）或飞行捕食,它主要捕食个体较大的甲虫;（4）角菊头蝠（Rhinolophus cornutus)主要在较密集树木中（枝叶间）,农田及树木周围捕食型较小的翼拍动昆虫;（5）三叶蹄幅（Aselliscus wheeleri)是在树木,灌丛或在其周围空间内捕食较小的翼拍动昆虫,但其食性可能菊头蝠不同,根据以上研究结果,认为这5种蝙蝠的取食生态位存在着明显的分化。     

Visual Evaluation and Recognition of Hosts by the Tick Parasitoid, Ixodiphagus hookeri (Hymenoptera: Encyrtidae)

The role of host size, movement, feeding status, color, and species in the visual host evaluation and recognition behavior of the tick parasitoid, Ixodiphagus hookeri Howard was investigated. Freshly emerged female parasitoids were subjected to a choice bioassay, where the test materials were placed in sealed vials and the vials placed in a Petri dish. When presented with A. variegatum live and mummified nymphs, females examined: larger nymphs significantly longer than smaller nymphs, fed nymphs significantly longer than unfed nymphs, dead and live nymphs for similar lengths of time, and grey live nymphs and yellow-brown and dark brown mummified nymphs for similar lengths of time. The total number of visits to vials containing these test materials were also not significantly different, except there were significantly more visits to yellow-brown mummies when compared to the number of visits to dark brown mummies. When presented with A. variegatum (host) and R. appendiculatus (nonhost) nymphs, the females examined A. variegatum nymphs significantly longer than R. appendiculatus nymphs. The total number of visits to vials containing A. variegatum nymphs were significantly more than the visits to the vials containing R. appendicualtus nymphs. Furthermore, females spent significantly more total examination time per visit on larger and fed A. variegatum nymphs when compared to smaller and unfed nymphs, respectively. Direct and indirect detection were significant when females were presented with fed versus unfed A. variegatum nymphs, grey nymphs versus yellow-brown mummies, and R. appendiculatus versus A. variegatum nymphs. Direct and indirect detection for the rest of the bioassays were not significantly different. Finally, The percentages of females contacting large fed A. variegatum nymphs first were significantly different from those of females contacting small unfed R. appendiculatus nymphs first. The firstcontact percentages for the rest of the bioassays were not significantly different.     

PYTHIUM SYLVATICUM鉴定及其专一性PCR引物

从杭州采集的水稻、棉花和大豆猝倒苗中分离到国内新记录腐霉种Pythium sylvaticum。该腐霉为异宗配合种,菌丝膨大体球形或柠檬形,雄器异丝生,藏卵器光滑,每个藏卵器上1~3个雄器,雄器常在接近藏卵器处形成二叉状分枝,卵孢子不满器。测定了该种4 个菌株的核糖体内转录间隔区(ITS)的序列,根据与59种腐霉ITS序列的比较,设计了P. sylvaticum种专一性引物PSF1和PSR2。实际结果表明:该引物能从11种共14株腐霉DNA中特异性地扩增P. sylvaticum,从而与其它10种腐霉区分。     

小麦及其相关物种rbcL基因序列的比较研究

用4个抗白粉病小麦品系构建了一个混合cDNA文库,从该文库中分离到一个新的小麦rbcL基因全长cDNA克隆。至此,已经有3个不同的小麦rbcL基因序列被报道,新rbcL基因cDNA与以前的2个序列分别有1个和3个碱基的差异。新的cDNA长1519bp(基因库查询号：AY328025)。同源性比较发现,新的小麦rbcL基因的cDNA序列与以前报告的小麦rbcL基因的cDNA序列(gi：344052)有一个碱基的差异,从而导致所编码的多肽在144位由Tyr变为Cys。进一步比较分析了在相关物种中rbcL基因的cDNA序列,结果显示,rbcL基因的编码区在不同属的物种间高度保守,并从分子水平表明小麦与大麦、新麦草、赖草、披碱草属等的亲源关系比与水稻、玉米等的近。     

不同品种槟榔果实性状及其槟榔碱含量的比较研究

通过性状比较和差异显著性检验,从形态学与生物化学两个水平研究了海南5个常见槟榔栽培种之间果实性状变化及其槟榔碱含量的变化。结果表明:(1)海南槟榔5个品种间果实性状都不同,其中以品种A、B、D的果实品质达到国家药典规定的一级标准,品种C、E达到二级标准;(2)品种E的叶面积、产量(座果数×单果重)最大,通过差异显著性检验,表明植株的产量与叶面积呈正相关;(3)5个品种中以品种B的槟榔碱含量最大(0.4451％),其次为品种E、C、D、A。其中品种A与B、A与E、B与D、B与E之间差异显著;(4)长、短蒂花品种之间槟榔碱含量差异不显著;(5)槟榔碱含量与其果实性状之间无显著相关性;(6)槟榔碱含量与营养成分间无显著相关性。     

武夷山毛竹天然林生物量与能量分配规律及其与人工林的比较研究

以武夷山国家自然保护区核心区天然毛竹林为研究对象,应用生物量优化模型对天然毛竹林生物量、能量的分配规律进行研究,结果表明:①毛竹天然林生物量按组分秆、枝、叶、竹蔸、鞭根的分配规律为5585.956、1120.456、387.453、1148.785、2827.099g·m~(-2),所占比例依次为50.46％、10.12％、3.50％、10.38％、25.54％,能量现存量按组分分别为112171.60、21694.0、7532.8、21796.8、52089.3kJ·m~(-2),所占比例依次为51.70％、10.00％、3.47％、10.05％、24.78％;②毛竹天然林生物量按龄级Ⅰ度、Ⅱ度、Ⅲ度、Ⅳ度、Ⅴ度及以上竹的分配规律为2151.845、1799.441、1184.757、1010.021、4923.684g·m~(-2),所占比例依次为19.44％、16.26％、10.70％、9.12％、44.48％。能量现存量按龄级分别为47465.97、40232.99、26502.84、17737.74、102488.8kJ·m~(-2),所占比例依次为20.25％、17.16％、11.30％、7.57％、43.72％。在此基础上,将毛竹天然林与人工林进行了比较分析。且为毛竹林的丰产培育提出了科学依据。     

东北过伐林区四种森林类型的物种多样性比较研究

运用无偏对应分析(DCA)、群落本质多样性排序和方差分析的方法,研究了东北过伐林区吉林省汪清林业局境内的四种森林类型——针阔混交林、阔叶混交林、柞木林和长白落叶松人工林的林分层次的植物物种多样性间的差异。从4种类型下层植被多样性指数的比较结果来看,针阔混交林最高,阔叶混交林和落叶松人工林次之,柞木林最低。最后提出了部分经营建议。     

2种蜜蜂和4种胡蜂蜂毒明肽基因比较

从中华蜜蜂、意大利蜜蜂和大胡蜂、墨胸胡蜂、额斑黄胡蜂、亚非马蜂6种蜂的雌成蜂毒腺中快速抽提总RNA,用RT—PCR方法分别扩增各得到大小约为150bp的cDNA片段,进一步将这6个片段克隆人pGEM^5—T easy载体,进行测序和序列分析。结果表明,所扩增得到的6个片段长度均为141bp,均为编码蜂毒apamin前体的cDNA。序列比较发现,中华蜜蜂、大胡蜂、墨胸胡蜂和亚非马蜂序列完全一样,都与已发表意大利蜜蜂precursor of apamin核苷酸序列具有95％同源性,氨基酸序列具有95％的同源性。额斑黄胡蜂和意大利蜜蜂precursor of apamin核苷酸序列完全一样。本研究首次从中华蜜蜂与几种胡蜂中克隆到蜂毒precursor of apamin基因,并发现胡蜂科与蜜蜂科来源的蜂毒明肽序列是完全保守的。     

滇蛙和昭觉林蛙的形态差异及其潜在的适应意义

以比较解剖学的方法,观察和比较了采自1997年8月-2000年9月的滇蛙(♂16,♀14)和昭觉林蛙(♂17,♀17)标本的外部形态、肌肉和骨骼。结果显示,两种蛙的皮肤颜色不同;滇蛙的鳞骨比昭觉林蛙的发达;滇蛙雄性个体具声囊,而昭觉林蛙则无;滇蛙和昭觉林蛙的肱三头肌、股三头肌和胫部的肌肉有显著或极显著差异;昭觉林蛙的四肢骨骼较滇蛙的细长,腰带坐骨结节较突出,髋臼也较大;两种蛙头部扩大的骨骼不同;滇蛙腹直肌具腱划4条,昭觉林蛙5条。两种蛙的这些形态差异与其栖息的小生境及生活方式的差异相适应。