Toward the active conformation of insulin: stereospecific modulation of a structural switch in the B chain

How insulin binds to the insulin receptor has long been a subject of speculation. Although the structure of the free hormone has been extensively characterized, a variety of evidence suggests that a conformational change occurs upon receptor binding. Here, we employ chiral mutagenesis, comparison of corresponding d and l amino acid substitutions, to investigate a possible switch in the B-chain. To investigate the interrelation of structure, function, and stability, isomeric analogs have been synthesized in which an invariant glycine in a beta-turn (Gly(B8)) is replaced by d- or l-Ser. The d substitution enhances stability (DeltaDeltaG(u) 0.9 kcal/mol) but impairs receptor binding by 100-fold; by contrast, the l substitution markedly impairs stability (DeltaDeltaG(u) -3.0 kcal/mol) with only 2-fold reduction in receptor binding. Although the isomeric structures each retain a native-like overall fold, the l-Ser(B8) analog exhibits fewer helix-related and long range nuclear Overhauser effects than does the d-Ser(B8) analog or native monomer. Evidence for enhanced conformational fluctuations in the unstable analog is provided by its attenuated CD spectrum. The inverse relationship between stereospecific stabilization and receptor binding strongly suggests that the B7-B10 beta-turn changes conformation on receptor binding.     

Crystallization and preliminary X-ray crystallographic analysis of spruce budworm antifreeze protein.

Antifreeze proteins have the ability to bind to ice with high affinity and inhibit further crystal growth. The insect antifreeze protein from spruce budworm exhibits very high thermal hysteresis activity and is implicated in the protection of overwintering larvae from freezing. This protein has been crystallized in 20-25% polyethylene glycol (Mr 6000), 0.4 M NaCl, 0.1 M Tris-HCl, pH 8.5, by vapor diffusion using the hanging drop method. The resulting crystals are very thin (typically <0.01 mm in the shortest dimension), and only after repeated seeding could crystals be grown large enough for data collection using synchrotron radiation. The crystals belong to the monoclinic space group C2, with cell dimensions a = 82.28 A, b = 62.29 A, c = 63.63 A, and beta = 113.7 degrees. Molecules in the asymmetric unit are related by a twofold axis of symmetry with two molecules present. Native data to a resolution of 2.6 A have been collected with 90.3% completeness and a Rsym of 6.9%.     

Chromosomal Location and Comparative Genomics Analysis of Powdery Mildew Resistance Gene Pm51 in a Putative Wheat-Thinopyrum ponticum Introgression Line

Powdery mildew (PM) is a very destructive disease of wheat (Triticum aestivum L.). Wheat-Thinopyrum ponticum introgression line CH7086 was shown to possess powdery mildew resistance possibly originating from Th. ponticum. Genomic in situ hybridization and molecular characterization of the alien introgression failed to identify alien chromatin. To study the genetics of resistance, CH7086 was crossed with susceptible genotypes. Segregation in F₂ populations and F_2:3 lines tested with Chinese Bgt race E09 under controlled conditions indicated that CH7086 carries a single dominant gene for powdery mildew resistance. Fourteen SSR and EST-PCR markers linked with the locus were identified. The genetic distances between the locus and the two flanking markers were 1.5 and 3.2 cM, respectively. Based on the locations of the markers by nullisomic-tetrasomic and deletion lines of ‘Chinese Spring’, the resistance gene was located in deletion bin 2BL-0.89-1.00. Conserved orthologous marker analysis indicated that the genomic region flanking the resistance gene has a high level of collinearity to that of rice chromosome 4 and Brachypodium chromosome 5. Both resistance specificities and tests of allelism suggested the resistance gene in CH7086 was different from previously reported powdery mildew resistance genes on 2BL, and the gene was provisionally designated PmCH86. Molecular analysis of PmCH86 compared with other genes for resistance to Bgt in the 2BL-0.89-1.00 region suggested that PmCH86 may be a new PM resistance gene, and it was therefore designated as Pm51. The closely linked flanking markers could be useful in exploiting this putative wheat-Thinopyrum translocation line for rapid transfer of Pm51 to wheat breeding programs.     

长沙市不同污染程度区域桂花和香樟叶表面PM2.5吸附量及其影响因素

为阐释不同污染程度下城市绿化植物吸滞PM_2.5机理、解析污染物来源,应用气溶胶再发生器定量测定长沙市常见的2种园林绿化树种(桂花和香樟)植物叶片PM_2.5吸附量,同时应用原子力显微镜(AFM)观察了不同污染区(交通区、文教区、清洁区)植被的叶表面微形态特征,使用离子色谱仪测定样品中水溶性离子含量.结果表明: 污染程度与植物叶表面PM_2.5吸附量呈正相关,不同植物单位叶面积PM_2.5吸附量全年均值表现为交通区(0.56±0.04 μg·cm^-2)＞文教区(0.48±0.06 μg·cm^-2)＞清洁区(0.33±0.02 μg·cm^-2),植物单位叶面积PM_2.5吸附量季节变化为冬季(0.70±0.10 μg·cm^-2)＞春季(0.43±0.14 μg·cm^-2)＞秋季(0.39±0.12 μg·cm^-2)＞夏季(0.31±0.09 μg·cm^-2),桂花的单位叶面积PM_2.5吸附量大于香樟;污染程度轻的区域的植物叶片比较光滑,污染程度重的区域的叶片较粗糙,植物粗糙度排序为交通区(195.45±16.09 nm)＞文教区(176.99±8.45 nm)＞清洁区(131.88±12.98 nm);不同污染程度地区PM_2.5离子含量均表现为冬季最大,其次是春季和秋季,夏季最低;3个污染区PM_2.5离子成分均以Na⁺、NH₄⁺、Cl^-和Br^-这4种离子为主,不同程度污染区PM_2.5污染均以移动源污染为主.     

Peroxisome proliferator-activated receptor alpha-responsive genes induced in the newborn but not prenatal liver of peroxisomal fatty acyl-CoA oxidase null mice.

Mice deficient in fatty acyl-CoA oxidase (AOX(-/-)), the first enzyme of the peroxisomal beta-oxidation system, develop specific morphological and molecular changes in the liver characterized by microvesicular fatty change, increased mitosis, spontaneous peroxisome proliferation, increased mRNA and protein levels of genes regulated by peroxisome proliferator-activated receptor alpha (PPARalpha), and hepatocellular carcinoma. Based on these findings it is proposed that substrates for AOX function as ligands for PPARalpha. In this study we examined the sequential changes in morphology and gene expression in the liver of wild-type and AOX(-/-) mice at Embryonic Day 17.5, and during postnatal development up to 2 months of age. In AOX(-/-) mice high levels of expression of PPARalpha-responsive genes in the liver commenced on the day of birth and persisted throughout the postnatal period. We found no indication of PPARalpha activation in the livers of AOX(-/-) mice at embryonic age E17.5. In AOX(-/-) mice microvesicular fatty change in liver cells was evident at 7 days. At 2 months of age livers showed extensive steatosis and the presence in the periportal areas of clusters of hepatocytes with abundant granular eosinophilic cytoplasm rich in peroxisomes. These results suggest that the biological ligands for PPARalpha vis a vis substrates for AOX either are not functional in fetal liver or do not cross the placental barrier during the fetal development and that postnatally they are likely derived from milk and diet.     

Insulin-producing cells from human adipose tissue-derived mesenchymal stem cells detected by atomic force microscope

We successfully differentiated human adipose tissue-derived mesenchymal stem cells (haMSCs) into insulin-producing cells (IPCs) in vitro and did not use any insulin which might be absorbed by cells during in vitro culture. Expression of insulin gene was massively increased by 28,000-fold at day 12 compared with haMSCs (P < 0.05). IPCs could secrete insulin after glucose was stimulated. The higher the concentration of glucose, the more production of insulin was noted. We reported AFM images of IPCs for the first time. AFM images showed that the sizes of cells were similar to each other, and all IPC surface had a porous structure in the cytoplasm area. In sugar-free group, the size of holes was similar (diameter, 1,086.98 ± 156.70 nm; depth, 185.22 ± 52.14 nm). In higher sugar-stimulated group, there were more holes with bigger diameter and smaller depth. (diameter, 3,183.65 ± 2,229.18 nm; depth 109.42 ± 56.26 nm, P < 0.05). We found that the hole diameter and depth could change with the concentration of glucose in media. Concurrently, laser scanning confocal microscopy images indicated that cortical actin network beneath plasma membrane in IPCs was dense and continuous. After glucose stimulation, we found the actin web depolymerized and became discontinuous in IPCs. We speculated that diameter augmentation of holes located in the cytoplasm area in IPCs was one manifestation of excytosis increase.     

云南松三种同域共存切梢小蠹梢转干期的空间分布格局

分布在我国西南地区的横坑切梢小蠹,云南切梢小蠹和短毛切梢小蠹同域危害寄主云南松,给林业生产带来巨大损失。为探讨同域切梢小蠹种群在共存下对其空间分布格局的影响,采用传统聚集指标法和地统计学方法研究了三者在梢转干期不同受害云南松纯林树冠中的空间分布型。结果表明重度受害样地中云南切梢小蠹种群密度显著高于横坑切梢小蠹,在轻度受害样地则相反;传统聚集指标法结果显示同域共存的3种切梢小蠹种群在不同受害程度云南松中均为聚集分布,横坑切梢小蠹和云南切梢小蠹聚集是由环境因素和昆虫本身的聚集习性引起;地统计学结果表明除重度受害样地中短毛切梢小蠹呈随机分布外,其余切梢小蠹在不同种群密度下均呈聚集分布;除重度受害样地横坑切梢小蠹外,其他小蠹的空间依赖范围为4.01—7.45 m。横坑切梢小蠹和云南切梢小蠹在不同受害林分中拟合的半变异函数模型在球形模型和高斯模型之间转换。同域共存关系不影响不同种群密度下的切梢小蠹种群空间分布类型,但影响其半变异函数模型和理论参数。