Structural transitions upon ligand binding in a cooperative dimeric hemoglobin

Comparison of the 2.4 angstrom resolution crystal structures of dimeric clam hemoglobin in the deoxygenated and carbon-monoxide liganded states shows how radically different the structural basis for cooperative oxygen binding is from that operative in mammalian hemoglobins. Heme groups are in direct communication across a novel subunit interface formed by the E and F helices. The conformational changes at this interface that accompany ligand binding are more dramatic at a tertiary level but more subtle at a quaternary level than those in mammalian hemoglobins. These findings suggest a cooperative mechanism that links ligation at one subunit with potentiation of affinity at the second subunit.     

Direct observation of global protein motion in hemoglobin and myoglobin on picosecond time scales

Picosecond phase-grating spectroscopy is highly sensitive to density changes and provides a new holographic approach to the study of protein dynamics. Photodissociation of carbon monoxide from heme proteins induces a well-defined transition from a ligated to a deoxy structure that is important to hemoglobin and myoglobin functionality. Grating spectroscopy was used to observe protein-driven density waves on a picosecond time scale after carbon monoxide dissociation. This result demonstrates that global tertiary structure changes of proteins occur on an extremely fast time scale and provides new insight into the biomechanics of deterministic protein motion.     

Cat hemoglobin: pH-dependent cooperativity of oxygen binding

Cat hemoglobin has a lower cooperativity and oxygen affinity than most mammalian hemoglobins. In contrast to the usual invariance of cooperativity with pH, a rise in cooperativity with pH is predicted by the allosteric model for low-affinity hemoglobins. Such a pH-dependent cooperativity for cat hemoglobin has been found.     

BRCA2 function in DNA binding and recombination from a BRCA2-DSS1-ssDNA structure

Mutations in the BRCA2 (breast cancer susceptibility gene 2) tumor suppressor lead to chromosomal instability due to defects in the repair of double-strand DNA breaks (DSBs) by homologous recombination, but BRCA2's role in this process has been unclear. Here, we present the 3.1 angstrom crystal structure of a approximately 90-kilodalton BRCA2 domain bound to DSS1, which reveals three oligonucleotide-binding (OB) folds and a helix-turn-helix (HTH) motif. We also (i) demonstrate that this BRCA2 domain binds single-stranded DNA, (ii) present its 3.5 angstrom structure bound to oligo(dT)9, (iii) provide data that implicate the HTH motif in dsDNA binding, and (iv) show that BRCA2 stimulates RAD51-mediated recombination in vitro. These findings establish that BRCA2 functions directly in homologous recombination and provide a structural and biochemical basis for understanding the loss of recombination-mediated DSB repair in BRCA2-associated cancers.     

Hemoglobin Portland 1: a new human hemoglobin unique in structure

A new hemoglobin (Hb), Portland 1, has been found in a newborn infant having multiple congenital anomalies and complex autosomal chromosomal mosaicism. The new hemoglobin has a unique tetrameric structure (molecular weight, 66,000) composed of two pairs of different types of chains, neither of which is alpha, gamma(2)x(2). The x-chain of Hb Portland 1 may be a new type of hemoglobin chain, but the available evidence suggests that it may be identical with the epsilon chain. We suggest that Hb Portland 1 is an embryonic hemoglobin that persisted until after birth in relatively large amounts in this patient.     

Anemia in domestic cats: effect on hemoglobin components and whole blood oxygenation

Phenylhydrazine-induced anemia in the domestic cat results in an increase in minor, high oxygen affinity hemoglobin B components and an accompanying decrease in the major, low affinity B component. This change is accompanied by an unusually large increase in erythrocytic adenosine triphosphate and 2,3-diphosphoglycerate, a slight decrease in the oxygen affinity of whole blood, and a large decrease in the Hill constant.     

Reserpine: effect on structure of heart muscle

We examined the ultrastructure of hearts from dogs given reserpine intramuscularly for 4 days, and from untreated dogs. Sections of the myocardium from treated dogs invariably revealed mitochondrial abnormalities at the 5th and 14th days. These included fragmentation and loss of structure of the cristae, and cyst formation. The appearance at 25 days in the treated as well as in all the untreated dogs was normal. We concluded that reserpine in the dose used produces marked structural changes in the mitochondria of heart muscle, and that these changes are reversible. These changes may account for the myocardial depression sometimes seen after administration of reserpine.     

水中亚硝酸盐对彭泽鲫血红蛋白及高铁血红蛋白的影响

调查和监测了60口优质鱼类养殖池塘水质理化因子和生物因子共31项，结果发现，多发病的鱼塘亚硝酸盐含量比少发病的鱼塘高，其含量均值分别为0.176,0.095mg/L,以彭泽鲫（Carassius auratus)为试验材料，测定亚硝酸盐对血红蛋白的毒性影响，结果表明，鲫血液中的高铁血红蛋白（MHb) 随NO2－N浓度的增加呈指数递增关系，1.8mg/L和0.8mg/LNO2-N分别为48h 和 96h毒性影响的临界值，养殖水体增加足量溶氧，适量的氧化剂，氯离子和硝化细菌，可降低亚硝酸盐的含量。     

The fine-scale structure of recombination rate variation in the human genome

The nature and scale of recombination rate variation are largely unknown for most species. In humans, pedigree analysis has documented variation at the chromosomal level, and sperm studies have identified specific hotspots in which crossing-over events cluster. To address whether this picture is representative of the genome as a whole, we have developed and validated a method for estimating recombination rates from patterns of genetic variation. From extensive single-nucleotide polymorphism surveys in European and African populations, we find evidence for extreme local rate variation spanning four orders in magnitude, in which 50% of all recombination events take place in less than 10% of the sequence. We demonstrate that recombination hotspots are a ubiquitous feature of the human genome, occurring on average every 200 kilobases or less, but recombination occurs preferentially outside genes.     

农业机械化对我国粮食生产的影响:产出效应、结构效应和外溢效应

改革开放以来,我国农业机械化发展迅速,农机总动力显著增长,农机结构不断优化,机械化作业水平快速提高。作为一种高效的劳动节约型技术,农业机械化提高了粮食生产的劳动生产率和土地产出率。同时推动了要素投入结构优化和种植结构调整,使部分区域种植结构呈"趋同化""趋粮化"发展;促进了种粮主体、农机投资和农机作业服务主体、兼业和转移就业人员等多方式增收。通过农业机械化投资,以投资锁定效应、沉淀成本促进了新型农业经营主体形成和粮食规模经营;并以劳动节约、效率提升实现了节本增效,提升了粮食基础竞争力,推动了农业技术进步和发展方式转变。农业机械化的产出效应、结构效应和外溢效应已经深刻影响我国农业发展格局。因此,加大对农业机械化技术研发、应用和推广的支持,对农机具购置和农机生产作业服务予以补贴,不失为提高农业发展质量和效益、推动农业发展方式转变和农业现代化的一种可选路径。     

Tetanus toxin: fine structure localization of binding sites in striated muscle

When striated muscle from mice poisoned with purified tetanus neurotoxin was incubated with tetanus antitoxin labeled with horseradish peroxidase and stained for peroxidase activity, an electron-opaque reaction product was found in the transverse and terminal sacs of the longitudinal elements of the sarcotubular system. Demonstration of toxin in this location suggests that it acts by interfering with contraction coupling or mechanisms of contraction-relaxation.     

Cigarette smoke: the effect of residue on mitochondrial structure

Cigarette smoke residue is ciliatoxic to Tetrahymena pyriformis. Principal sites of activity are the mitochondria of the cell. The internal membranes of the mitochondria are degraded with time, correlating well with loss of ciliary activity and cell death.     

Gelation of sickle cell hemoglobin: effects of hybrid tetramer formation in hemoglobin mixtures

The altered gelation behavior found in mixtures of sickle cell hemoglobin with other hemoglobins is due to the formation of hybrid hemoglobin tetramers from unlike dimers. The hemoglobins need not possess the deoxy quaternary structure for gelation to occur; liganded forms are also capable of participation in gelation.     

SMA智能控制装置及结构地震反应控制分析

为了获得一种性能优良的结构抗震用控制装置,通过利用SMA(Shape Memory Alloy)弹性模量随温度变化特性,设计了一种新型SMA智能控制装置,并给出了SMA智能控制装置最大输出控制力和等效刚度的计算公式。最后,针对某3层框架结构,分别在未控、主动控制和SMA智能控制3种情况下,进行了地震时程仿真分析。计算结果表明:SMA智能控制装置可以有效降低结构地震反应幅值,控制效果接近主动控制效果,是一种较好的结构抗震用控制装置。     

Crystal structure analysis of deamino-oxytocin: conformational flexibility and receptor binding

Two crystal structures of deamino-oxytocin have been determined at better than 1.1A resolution from isomorphous replacement and anomalous scattering x-ray measurements. In each of two crystal forms there are two closely related conformers with disulfide bridges of different chirality, which may be important in receptor recognition and activation.     

Crystal structure of naphthalene dioxygenase: side-on binding of dioxygen to iron

Binding of oxygen to iron is exploited in several biological and chemical processes. Although computational and spectroscopic results have suggested side-on binding, only end-on binding of oxygen to iron has been observed in crystal structures. We have determined structures of naphthalene dioxygenase that show a molecular oxygen species bound to the mononuclear iron in a side-on fashion. In a complex with substrate and dioxygen, the dioxygen molecule is lined up for an attack on the double bond of the aromatic substrate. The structures reported here provide the basis for a reaction mechanism and for the high stereospecificity of the reaction catalyzed by naphthalene dioxygenase.     

果蔗螟虫药剂防治效果

果蔗螟虫是果蔗生长期的主要害虫,其发生种类多,为害时间长。蔗螟以二化螟、大螟、二点螟为主,其中二化螟占螟虫总量的90%以上,在苗期至伸长期可持续为害,造成产量损失与糖分下降。据调查,在果蔗生长期若不防治螟虫,植株螟害率可高达50%以上。我县蔗农习惯频繁滥用久效磷等高毒农药防治蔗螟,导致果蔗农药残毒超标,影响食用安全性。为此,2000、2001年我们尝试在果蔗伸长期采用一些中低毒农药防治蔗螟,取得了较好的效果。     

广东省反贫困治理结构及其构建

结合国内外反贫困治理结构的理论与实践，提出了建立广东省反贫困治理结构的设想，包括反贫困的目标与战略、扶贫管理体制与资金运行机制、政策和法规、贫困人口的参与和组织。