An improved loopless mounting method for cryocrystallography

Based on a recent loopless mounting method, a simplified loopless and bufferless crystal mounting method is developed for macromolecular crystallography. This simplified crystal mounting system is composed of the following components: a home-made glass capillary, a brass seat for holding the glass capillary, a flow regulator, and a vacuum pump for evacuation. Compared with the currently prevalent loop mounting method, this simplified method has almost the same mounting procedure and thus is compatible with the current automated crystal mounting system. The advantages of this method include higher signal-to-noise ratio, more accurate measurement, more rapid flash cooling, less x-ray absorption and thus less radiation damage to the crystal. This method can be extended to the flash-freeing of a crystal without or with soaking it in a lower concentration of cryoprotectant, thus it may be the best option for data collection in the absence of suitable cryoprotectant. Therefore, it is suggested that this mounting method should be further improved and extensively applied to cryocrystallographic experiments.     

The balance of flexibility and rigidity in the active site residues of hen egg white lysozyme

The crystallographic temperature factors(B factor) of individual atoms contain important information about the thermal motion of the atoms in a macromolecule.Previously the theory of flexibility of active site has been established based on the observation that the enzyme activity is sensitive to low concentration denaturing agents.It has been found that the loss of enzyme activity occurs well before the disruption of the three-dimensional structural scaffold of the enzyme.To test the theory of conformational flexibility of enzyme active site,crystal structures were perturbed by soaking in low concentration guanidine hydrochloride solutions.It was found that many lysozyme crystals tested could still diffract until the concentration of guanidine hydrochloride reached 3 M.It was also found that the B factors averaged over individually collected data sets were more accurate.Thus it suggested that accurate measurement of crystal temperature factors could be achieved for medium-high or even medium resolution crystals by averaging over multiple data sets.Furthermore,we found that the correctly predicted active sites included not only the more flexible residues,but also some more rigid residues.Both the flexible and the rigid residues in the active site played an important role in forming the active site residue network,covering the majority of the substrate binding residues.Therefore,this experimental prediction method may be useful for characterizing the binding site and the function of a protein,such as drug targeting.     

PPTA与PBA共混纤维的结构性能

随着聚对苯二甲酰对苯二胺(简称 PPTA)纤维在军工、宇航、航空、交通运输、通讯及其它部门的日益广泛应用,对其性能特别是模量,提出了更高的要求。为了提高 PPTA 纤维的模量,本文利用聚对苯甲酰胺(简称 PBA)纤维的高模量特性,将PPTA 与 PBA 聚合体进行共混纺丝,制成共混纤维。当 PBA 加入量为3—10％时,纤维的强度基本不变,共混纤维经热处理后模量有较大的提高。且含水率进一步下降,从而可改善复合材料的力学性能。     

T细胞功能学与结构免疫学结合方法鉴定HLA-A2限制性的细胞毒性T淋巴细胞表位富集区

 T细胞表位在抗病毒的T细胞免疫中发挥核心作用,目前已在多种病原微生物的蛋白序列上发现存在T细胞表位的聚集现象。本文建立了一套功能学与结构学结合的策略鉴定病原体上细胞毒性T细胞(Cytotoxic T Lymphocyte,CTL)表位富集区的方法,并以严重急性呼吸道综合征(SARS)相关冠状病毒(SARS-CoV)的M蛋白为例,成功地鉴定了一个HLA-A2限制性的表位富集区。首先通过生物信息学的方法预测并合成M蛋白跨膜区的HLA-A2潜在结合多肽,通过体外复性实验和T2细胞结合实验验证多肽与HLA-A2的结合力;然后在HLA-A2.1/Kb转基因小鼠中检测这些多肽的免疫原性;最后通过X射线衍射技术,成功解析了其中一条多肽与HLA-A^*0201的复合物结构,其结构显示该多肽具有典型的HLA-A^*0201表位的结构特点,但却呈现出与以往鉴定多肽不同的构象和锚定残基。本文对于理解机体对SARS-CoV等病原体产生的T细胞免疫反应,以及为更广泛的人群设计T细胞疫苗具有重要意义。     

红色核桃仁种皮提取物紫外-可见光谱和质谱分析

采用紫外-可见光谱和高效液相色谱/电喷雾质谱(HPLC-ESI-MSn)联用技术对红色核桃仁种皮提取物进行了初步分析.红色核桃仁种皮的盐酸乙醇提取物在560和591 nm处有2个吸收峰,经过醋酸铅沉淀和薄层层析纯化后在340,370,552和585 nm处有4个吸收峰,说明红色核桃仁种皮中含有花色苷物质,红色核桃仁种皮的盐酸乙醇提取物经HPLC-ESI-MSn(负离子模式扫描)分析后获得m/z为301,481,633,783,785和951等分子离子峰,其对应的物质为鞣花酸、没食子酰基-鞣花酰基葡萄糖、二鞣花酰基葡萄糖、二没食子酰基-鞣花酰基葡萄糖和鞣花酰基-像椀酰基匍萄糖等鞣花单宁.     

109份丰产核桃单株坚果表型多样性分析及性状评价

【目的】果实表型分析和评价是良种选育的基础,分析核桃(Julans regia)坚果表型多样性并开展性状综合评价,可筛选出具有优良坚果性状的核桃品系。【方法】以北京农林科学院核桃选种圃109份丰产性较好的核桃单株为研究对象,测定其18个坚果表型性状,分析各性状的变异系数和遗传多样性,并进行方差、相关性、主成分、聚类和综合评价分析。【结果】(1)109份核桃坚果的18个表型性状变异均达到极显著水平,变异系数范围为4.70%～25.00%,遗传多样性指数范围为2.849～3.023,表征坚果大小和干质量的指标在个体间具有较高的离散程度,而坚果形状指标的个体间变异较小;(2)坚果各部分的干质量指标与反映坚果大小的指标均呈极显著正相关,坚果形状指标与坚果三径关系密切,种壳厚度和种壳干质量会显著影响坚果出仁率;(3)坚果大小、形状和外在品质指标能反映坚果表型性状的绝大部分信息,这3个主成分的累计贡献率达91.596%,以这3个主成分共筛选出几何平均直径、坚果体积、单果干质量、核仁干质量、球形度、壳厚、出仁率和体积出仁率等8个重要性状;(4)在欧氏距离9.0处将109份种质资源聚为4大类群,可用于...     

核桃仁中多酚类物质的液相/电喷雾质谱分析

利用HPLC-ESI-MSn方法对核桃(Juglans regia L.)仁中多酚类物质组成进行了分析,发现的多酚类物质有鞣花酰基葡萄糖4种异构体、橡椀酰基葡萄糖2种异构体、二鞣花酰基葡萄糖2种异构体、二没食子酰基葡萄糖2种异构体、鞣花酰基和橡椀酰基葡萄糖3种异构体.结果表明,采用HPLC-ESI-MSn方法可以对核桃仁中多酚类物质进行有效的分析.