Cleavage of the Carboxyl-Terminus of LEACS2, a Tomato 1-Aminocyclopropane-1-Carboxylic Acid Synthase Isomer, by a 64-kDa Tomato Metalloprotease Produces a Truncated but Active Enzyme

1-Aminocyclopropane-1-carboxylic acid （ACC） synthase （ACS） is the principal enzyme in phytohormone ethylene biosynthesis. Previous studies have shown that the hypervariable C-terminus of ACS is proteolytically processed in vivo. However, the protease responsible for this has not yet been identified. In the present study, we investigated the processing of the 55-kDa full-length tomato ACS （LeACS2） into 52-, 50- and 49-kDa truncated isoforms in ripening tomato （Lycopersicon esculentum Mill. cv. Cooperation 903） fruit using the sodium dodecyl sulfate-boiling method. Meanwhile, an LeACS2-processing protease was purified via multi-step column chromatography from tomato fruit. Subsequent biochemical analysis of the 64-kDa purified protease revealed that it is a metalloprotease active at multiple cleavage sites within the hypervariable C-terminus of LeACS2. N-terminal sequencing and matrix-assisted laser desorption/ionization time-of-flight analysis indicated that the LeACS2-processing metalloprotease cleaves at the C-terminal sites Lys^438, Glu^447, Lys^448, Asn^456, Ser^460, Ser^462, Lys^463, and Leu^474, but does not cleave the N- terminus of LeACS2. Four C-terminus-deleted （26-50 amino acids） LeACS2 fusion proteins were overproduced and subjected to proteolysis by this metalloprotease to identify the multiple cleavage sites located on the N-terminal side of the phosphorylation site Ser^460. The results indisputably confirmed the presence of cleavage sites within the region between the α-helix domain （H14） and Ser^460 for this metalloprotease. Furthermore, the resulting C-terminally truncated LeACS2 isoforms were active enzymatically. Because this protease could produce LeACS2 isoforms in vitro similar to those detected in vivo, it is proposed that this metalloprotease may be involved in the proteolysis of LeACS2 in vivo.     

人类巨细胞病毒、EB病毒和单纯疱疹病毒1型与慢性牙周炎的相关性研究

目的　研究人类巨细胞病毒( HCMV)、Epstein- Barr病毒( EBV)和单纯疱疹病毒1型( HSV- 1)与慢性牙周炎的相关性。方法　收集6 2例慢性牙周炎患者(男性2 7例,女性35例;平均年龄5 3岁)的牙周炎部位,轻度龈炎部位的龈下菌斑,提取DNA后使用巢式PCR检测HCMV、EBV和HSV- 1,比较分析它们在同一患者不同部位的检出率。结果　牙周炎部位的HCMV检出率为38.7% ,EBV的检出率为5 8.0 % ,HSV- 1的检出率为30 .6 % ,2种以上病毒合并感染的检出率为4 0 .3% ;轻度龈炎部位的HCMV检出率为12 .9% ,EBV为19.4 % ,HSV- 1为9.7% ,2种以上病毒合并感染的检出率为8.0 %。这3种病毒及其合并感染在牙周炎部位的检出率均高于轻度龈炎部位,差异有统计学意义( P<0 .0 5 )。结论　提示HCMV、EBV、HSV- 1与慢性牙周炎有相关性。     

低分子量肝素对妊高征大鼠肾脏病变的保护作用及机制初步探讨

目的:研究低分子量肝素(LMWH)对妊高征大鼠肾脏损伤的作用及其细胞内信号转导机制.方法:采用注射L-NAME方法制备妊高征动物模型,将妊娠大鼠随机分为正常妊娠组、妊高征组、LMWH治疗组,测定各组平均动脉压、尿蛋白、血肌酐及血尿素氮,观察LMWH对肾脏各指标的影响及肾脏出现的病理学变化;同时采用免疫组化、RT-PCR及Western Blot方法检测ERK1/2在各组的表达变化.结果:LMWH治疗组肾脏组织ERK1/2的蛋白及mRNA表达水平明显低于妊高征组(P＜0.01),而妊高征组肾脏组织ERK的蛋白及mRNA表达水平明显高于正常妊娠组(P＜0.01),ERK1与ERK2在各组大鼠肾脏中的表达无差异;治疗组平均动脉压及尿蛋白明显低于非治疗组(P＜0.05),但仍未达正常妊娠水平;HE染色和PAS染色为治疗组肾小球系膜增生、基底膜增厚较非治疗组明显减轻.ERK蛋白主要分布于肾小球中.结论:LMWH对妊高征大鼠肾脏损伤具有一定的防护作用,其机制可能是通过下调ERK1/2的表达来实现.     

Plasminogen/plasmin regulates c-fos and egr-1 expression via the MEK/ERK pathway

In this study, we showed that plasminogen (Plg) and plasmin (Pla) bind to lysine-binding sites on cell surface and trigger a signaling pathway that activates the mitogen-activated protein kinase (MAPK) MEK and ERK1/2, which in turn leads to the expression of the primary response genes c-fos and early growth response gene egr-1. Our data show that the Plg/Pla-stimulated steady-state mRNA levels of both genes reached a maximum by 30 min and then returned to basal levels by 1h. The gene induction was sensitive to both pharmacological and genetic inhibition of MEK. Leupeptin, a serine protease inhibitor, suppressed Pla but not Plg-induced c-fos and egr-1 expression, emphasizing the role played by the serine protease activity associated with Pla. Pre-incubation with cholera toxin completely blocked the Plg/Pla-induced gene expression, suggesting that another signaling pathway, which recruits G protein-coupled receptors, may also be involved. Furthermore, Plg/Pla also stimulated AP-1 and EGR-1 DNA-binding activities, which were abrogated by pharmacological inhibition of MEK. Altogether, these results suggest that Plg/Pla stimulates c-fos and egr-1 expression via activation of the MEK/ERK pathway.     

Overview of avian influenza DIVA test strategies

The use of vaccination in poultry to control avian influenza has been increasing in recent years. Vaccination has been primarily with killed whole virus-adjuvanted vaccines. Proper vaccination can reduce or prevent clinical signs, reduce virus shedding in infected birds, and increase the resistance to infection. Historically, one limitation of the killed vaccines is that vaccinated birds cannot be differentiated serologically from naturally infected birds using the commonly available diagnostic tests. Therefore, surveillance for avian influenza becomes much more difficult and often results in trade restrictions because of the inability to differentiate infected from vaccinated animals (DIVA). Several different DIVA strategies have been proposed for avian influenza to overcome this limitation. The most common is the use of unvaccinated sentinels. A second approach is the use of subunit vaccines targeted to the hemagglutinin protein that allows serologic surveillance to the internal proteins. A third strategy is to vaccinate with a homologous hemagglutinin to the circulating field strain, but a heterologous neuraminidase subtype. Serologic surveillance can then be performed for the homologous NA subtype as evidence of natural infection. The fourth strategy is to measure the serologic response to the nonstructural protein 1 (NS1). The NS1 protein is produced in large quantities in infected cells, but it is not packaged in the virion. Since killed vaccines for influenza are primarily made with whole virions, a differential antibody response can be seen between naturally infected and vaccinated animals. However, poultry vaccines are not highly purified, and they contain small amounts of the NS1 protein. Although vaccinated chickens will produce low levels of antibody to the NS1 protein, virus infected chickens will produce higher levels of NS1 antibody, and the two groups can be differentiated. All four DIVA strategies have advantages and disadvantages, and further testing is needed to identify the best strategy to make vaccination a more viable option for avian influenza.     

Electrostatic contributions to the kinetics and thermodynamics of protein assembly

The role of electrostatic interactions in the assembly of a native protein structure was studied using fragment complementation. Contributions of salt, pH, or surface charges to the kinetics and equilibrium of calbindin D(9k) reconstitution was measured in the presence of Ca(2+) using surface plasmon resonance and isothermal titration calorimetry. Whereas surface charge substitutions primarily affect the dissociation rate constant, the association rates are correlated with subdomain net charge in a way expected for Coulomb interactions. The affinity is reduced in all mutants, with the largest effect (260-fold) observed for the double mutant K25E+K29E. At low net charge, detailed charge distribution is important, and charges remote from the partner EF-hand have less influence than close ones. The effects of salt and pH on the reconstitution are smaller than mutational effects. The interaction between the wild-type EF-hands occurs with high affinity (K(A) = 1.3 x 10(10) M(-1); K(D) = 80 pM). The enthalpy of association is overall favorable and there appears to be a very large favorable entropic contribution from the desolvation of hydrophobic surfaces that become buried in the complex. Electrostatic interactions contribute significantly to the affinity between the subdomains, but other factors, such as hydrophobic interactions, dominate.     

Bt毒蛋白Cry1Ac在人造土壤中对赤子爱胜蚓毒理及生化影响

Bt毒素能通过转基因作物的花粉、根和残株进入土壤.为评估转基因作物对土壤动物的影响,本文模拟转基因棉的Bt毒素进入土壤的发生程度,用含不同浓度Bt毒蛋白Cry1Ac的人造土壤处理蚯蚓,测定蚯蚓存活率、重量变化及体内总蛋白含量和过氧化氢酶(CAT)、乙酰胆碱酯酶(AchE)、谷胱甘肽-S-转移酶(GST)和纤维素酶活性.结果表明,Bt毒蛋白对蚯蚓的生物量和生理水平影响均不明显,不存在急毒性和亚致死毒性影响,对蚯蚓比较安全.