Hyperactive antifreeze protein in a fish

Fish that live in the polar oceans survive at low temperatures by virtue of 'antifreeze' plasma proteins in the blood that bind to ice crystals and prevent these from growing. However, the antifreeze proteins isolated so far from the winter flounder (Pleuronectes americanus), a common fish in the Northern Hemisphere, are not sufficiently active to protect it from freezing in icy sea water. Here we describe a previously undiscovered antifreeze protein from this flounder that is extremely active (as effective as those found in insects) and which explains the resistance of this fish to freezing in polar and subpolar waters.     

Mimicry of ice structure by surface hydroxyls and water of a beta-helix antifreeze protein

Insect antifreeze proteins (AFP) are much more effective than fish AFPs at depressing solution freezing points by ice-growth inhibition. AFP from the beetle Tenebrio molitor is a small protein (8.4 kDa) composed of tandem 12-residue repeats (TCTxSxxCxxAx). Here we report its 1.4-A resolution crystal structure, showing that this repetitive sequence translates into an exceptionally regular beta-helix. Not only are the 12-amino-acid loops almost identical in the backbone, but also the conserved side chains are positioned in essentially identical orientations, making this AFP perhaps the most regular protein structure yet observed. The protein has almost no hydrophobic core but is stabilized by numerous disulphide and hydrogen bonds. On the conserved side of the protein, threonine-cysteine-threonine motifs are arrayed to form a flat beta-sheet, the putative ice-binding surface. The threonine side chains have exactly the same rotameric conformation and the spacing between OH groups is a near-perfect match to the ice lattice. Together with tightly bound co-planar external water, three ranks of oxygen atoms form a two-dimensional array, mimicking an ice section.     

TmAFP抗冻蛋白与冰面结合的稳定因素的研究

抗冻蛋白能特异的结合到冰晶的表面,抑制冰晶的生长和聚合,从而保护有机体不受大冰晶的伤害。基于蛋白质与冰晶之间的结构匹配关系和识别行为的研究,抗冻蛋白与冰面结合的相对稳定,依靠抗冻蛋白的特定氨基酸序列组成的空间结构恰好与冰面的空间结构能良好的相互匹配,并且又通过氢键作用,使抗冻蛋白与冰面结合得更加稳定,从而使蛋白质与冰面结合不易脱落。     

第一类抗冻蛋白与冰晶相互作用能的简单计算

第一类抗冻蛋白分子上的苏氨酸或缬氨酸对其在冰晶表面的吸附起主要作用,在此观点的基础上,认为抗冻蛋白分子在冰晶表面的吸附依赖于这些氨基酸上的甲基与冰晶的van der Waals相互作用,从理论上计算了第一类抗冻蛋白分子与冰晶的相互作用能,给出了几种第一类抗冻蛋白分子与冰晶的相互作用能.计算结果与实验结果符合较好.     

硅酸盐型防冻液的稳定性

针对硅酸盐型防冻液的不稳定性,研究考察防冻液配制过程中工艺参数对硅酸钠稳定性的影响.通过正交试验确定硅酸盐型防冻液配制的最佳工艺条件:硅酸钠的质量百分比为0.2%、添加硅酸钠时溶液的pH值为9、硅酸钠与稳定剂质量比为1∶1.5、硅酸钠加入时间控制在20min.     

Change of bacterial community in the Malan Ice Core and its relation to climate and environment

In order to understand the relationship between the community structure of bacteria in ice core and the past climate and environment, we initiated the study on the microorganisms in the three selected ice samples from the Malan ice core drilled from the Tibetan Plateau. The 16S ribosomal DNA (rDNA) molecules were directly amplified from the melt water samples, and three 16S rDNA clone libraries were established. Among 94 positive clones, eleven clones with unique restriction pattern were used for partial sequence and compared with eight reported sequences from the same ice core. The phylotypes were divided into 5 groups: alpha, beta, gamma proteobacteria; CFB, and other eubacteria group. Among them, there were many “typical Malan glacial bacteria“ pertaining to psychrophilies and new bacteria found in the ice core. At a longer time scale, the concentration distribution of “typical Malan glacial bacteria“ with depth showed negative correlation with temperature variations and was coincident with dirty layer. It implied the influence of temperature on the microbial record through impact on the concentrations of the “typical Malan glacial bacteria“. In addition, the nutrition contained in ice was another important factor controlling the distribution of microbial population in ice core section. Moreover, the result displayed an apparent layer distribution of bacterial community in the ice core section, which reflected the microbial response to the past climatic and environmental conditions at the time of deposition.     

Ice growth in supercooled solutions of antifreeze glycoprotein

Inhibition of ice growth in supercooled solution by certain proteins is vital to the survival of many living organisms. Some fish, native to both subzero northern and southern waters, have special proteins or glycoproteins in their blood serum that inhibit ice formation. Whereas these proteins have only a very small effect on the melting temperature of ice, the temperature of these fish can fall to nearly 1 K below the melting point before ice crystals grow. This phenomenon is called freezing hysteresis, in contrast to the normal colligative effect of solutes that depresses the equilibrium temperature, around which small changes lead to crystal growth or melting depending on sign. Some insects also exhibit a serum freezing hysteresis. We report the effects of different degrees of supercooling on the habit and rates of growth of ice crystals from solutions of these antifreeze glycoproteins (AFGPs). We find that the crystallization rate is up to five times greater than that in pure water.     

淡水鱼内脏中粗鱼油的酶法提取工艺研究

以淡水鱼的内脏为原料,对中性蛋白酶提取鱼油的工艺条件进行了研究,确定了最佳提取工艺为酶解温度48℃,酶解时间2.5 h,酶用量1 200 u/g,料液比1∶0.5.并对提取出的鱼油进行感官评价和理化指标的测定,结果鱼油的酸价为14.73,碘值132.76,过氧化值16.59 mmol/kg,皂化值180.54,不皂化值0.58,感官和理化等级均为二级.     

冬鲽鱼抗冻蛋白基因的人工合成

合成适合在棉花中表达的冬鲽鱼抗冻蛋白（Winter flounder antifreeze protein,Wf-AFP）基因.参照冬鲽鱼抗冻蛋白的氨基酸序列及棉花偏爱的密码子,重新设计适合在棉花中表达的Wf-AFP基因序列;根据此序列设计6条寡核苷酸引物,通过PCR方法将其拼接成完整的基因;克隆到pUCm-T载体上,转化大肠杆菌DH5α,抽提重组子进行酶切鉴定及序列分析.结果表明合成的Wf-AFP基因序列与设计方案完全相符,通过PCR介导的基因合成方法成功获得了适合在棉花中表达的冬鲽鱼抗冻蛋白基因.     

大型室内冰场冰温多点检测与数据融合

结合实际论述了室内冰场的冰温多点检测、温度传感器的工作原理，以及数据融合的方法。     

Stable expression of two variable surface glycoproteins by cloned Trypanosoma equiperdum

African trypanosomes are thought to evade the host immune system by periodically changing their variable surface glycoprotein (VSG). VSG genes are activated by a complex process involving the duplicative transposition of silent basic copy genes to one of several expression sites. These expression-linked copies (ELCs) of the VSG genes are also subject to regulation within expression sites by as yet unknown mechanisms. It is generally assumed that trypanosomes can express only one VSG gene at a time. Nevertheless, the finding that they contain multiple VSG gene expression sites suggests that multiple expression is possible. We show here that Trypanosoma equiperdum can stably express two VSG genes in a simple axenic culture system and that both antigens are present on the cell surface. The two antigens do not co-cap or form heterodimers. Their corresponding genes show no cross-hybridization and are situated in different telomere-linked expression sites. Northern blot analysis reveals that both genes are active in the double expressors.