Structural and functional analysis of two glutamate racemase isozymes from Bacillus anthracis and implications for inhibitor design

Glutamate racemase (RacE) is responsible for converting l-glutamate to d-glutamate, which is an essential component of peptidoglycan biosynthesis, and the primary constituent of the poly-gamma-d-glutamate capsule of the pathogen Bacillus anthracis. RacE enzymes are essential for bacterial growth and lack a human homolog, making them attractive targets for the design and development of antibacterial therapeutics. We have cloned, expressed and purified the two glutamate racemase isozymes, RacE1 and RacE2, from the B. anthracis genome. Through a series of steady-state kinetic studies, and based upon the ability of both RacE1 and RacE2 to catalyze the rapid formation of d-glutamate, we have determined that RacE1 and RacE2 are bona fide isozymes. The X-ray structures of B. anthracis RacE1 and RacE2, in complex with d-glutamate, were determined to resolutions of 1.75 A and 2.0 A. Both enzymes are dimers with monomers arranged in a "tail-to-tail" orientation, similar to the B. subtilis RacE structure, but differing substantially from the Aquifex pyrophilus RacE structure. The differences in quaternary structures produce differences in the active sites of racemases among the various species, which has important implications for structure-based, inhibitor design efforts within this class of enzymes. We found a Val to Ala variance at the entrance of the active site between RacE1 and RacE2, which results in the active site entrance being less sterically hindered for RacE1. Using a series of inhibitors, we show that this variance results in differences in the inhibitory activity against the two isozymes and suggest a strategy for structure-based inhibitor design to obtain broad-spectrum inhibitors for glutamate racemases.     

Decreased translation of p21waf1 mRNA causes attenuated p53 signaling in some p53 wild-type tumors

DNA damage induces cell cycle arrest through both Chk1 and the p53 tumor suppressor protein, the latter arresting cells through induction of p21^waf1 protein. Arrest permits cells to repair the damage and recover. The frequent loss of p53 in tumor cells makes them more dependent on Chk1 for arrest and survival. However, some p53 wild type tumor cell lines, such as HCT116 and U2OS, are also sensitive to inhibition of Chk1 due to attenuated p21^waf1 induction upon DNA damage. The purpose of this study is to determine the cause of this attenuated p21^waf1 protein induction. We find that neither the induction of p21^waf1 mRNA nor protein half-life is sufficient to explain the low p21^waf1 protein levels in HCT116 and U2OS cells. The induced mRNA associates with polysomes but little protein is made suggesting these two cell lines have a reduced rate of p21^waf1 mRNA translation. This represents a novel mechanism for disruption of the p53-p21^waf1 pathway as currently known mechanisms involve either mutation of p53 or reduction of p53 protein levels. As a consequence, this attenuated p21^waf1 expression may render some p53 wild type tumors sensitive to a combination of DNA damage plus checkpoint inhibition.     

α,α′-trehalose 6,6′-dibehenate in non-phospholipid-based liposomes enables direct interaction with trehalose, offering stability during freeze-drying

Trehalose is a well known protector of biostructures like liposomes and proteins during freeze-drying, but still today there is a big debate regarding its mechanism of action. In previous experiments we have shown that trehalose is able to protect a non-phospholipid-based liposomal adjuvant (designated CAF01) composed of the cationic dimethyldioctadecylammonium (DDA) and trehalose 6,6′-dibehenate (TDB) during freeze-drying [D. Christensen, C. Foged, I. Rosenkrands, H.M. Nielsen, P. Andersen, E.M. Agger, Trehalose preserves DDA/TDB liposomes and their adjuvant effect during freeze-drying, Biochim. Biophys. Acta, Biomembr. 1768 (2007) 2120-2129]. Furthermore it was seen that TDB is required for the stabilizing effect of trehalose. Herein, we show using the Langmuir-Blodgett technique that a high concentration of TDB present at the water-lipid interface results in a surface pressure around 67 mN/m as compared to that of pure DDA which is approximately 47 mN/m in the compressed state. This indicates that the attractive forces between the trehalose head group of TDB and water are greater than those between the quaternary ammonium head group of DDA and water. Furthermore, addition of trehalose to a DDA monolayer containing small amounts of TDB also increases the surface pressure, which is not observed in the absence of TDB. This suggests that even small amounts of trehalose groups on TDB present at the water-lipid interface associate free trehalose to the liposome surface, presumably by hydrogen bonding between the trehalose head groups of TDB and the free trehalose molecules. Hence, for CAF01 the TDB component not only stabilizes the cationic liposomes and enhances the immune response but also facilitates the cryo-/lyoprotection by trehalose through direct interaction with the head group of TDB. Furthermore the results indicate that direct interaction with liposome surfaces is necessary for trehalose to enable protection during freeze-drying.     

Quantification of local water and biomass in wild type PA01 biofilms by Confocal Raman Microspectroscopy

Confocal Raman Microspectroscopy (CRM) can be used as a tool for the in situ evaluation of the chemical composition of living, fully submerged, unstained biofilms. In this study the estimation of the local water content in Pseudomonas aeruginosa PA01 biofilms is given as an example. The ratio of the area of the O-H stretching vibration band at 3450 cm(-1), (water), to that of the C-H stretching bands at 2950 cm(-1) (biomass), was used to estimate the relative biofilm water content. The quantification of biofilm water and biomass was based on calibration curves generated from protein solutions. Water/biomass ratios (W:BR) equivalent to that of a 30% (w/v) protein solution were observed within some biofilm colonies.     

马抗SARS-CoV免疫球蛋白对SARS-CoV GZ-01株中和作用的研究

观察马抗SARS-CoV免疫球蛋白对SARS-CoV GZ-01毒株的中和作用,为马抗SARS-CoV免疫球蛋白用于SARS的治疗提供科学的依据。采用CPE、MTT测定马抗SARS-CoV免疫球蛋白对SARS-CoV GZ-01株的中和作用。结果显示,马抗SARS-CoV免疫球蛋白F(ab’)2治疗性抗体对SARS-CoV GZ-01株具有很好的中和作用,三批马抗SARS-CoV免疫球蛋白的CPE和MTT中和效价分别达到1:6400、1:6400、1:12800,且两种方法测得结果一致。     

CRF01-AE亚型人类免疫缺陷病毒的基因序列特征研究

从确诊的HIV-1感染者的全血样本中提取基因组DNA,经套式聚合酶链反应(PCR)扩增其gag蛋白P17/P24交界区基因片断后,将扩增产物进行纯化和测序,分析其氨基酸序列。进而了解所检出的病毒基因变异和分子流行病学特征。结果发现,HIV-1 CRF01-AE亚型病毒分别与3株不同来源的国际参考毒株具有紧密的亲缘关系,表明这些毒株可能分别由不同的传播路线进入我国大陆境内。     

云南十个少数民族的F13A01、FESFPS和vWA位点遗传多态分析

短串联重度序列（STR）是由几个碱基对作为核心单位串联重复形成的一类DNA序列,应用3个位点在同一反应体系中进行互不干扰的多重PCR,采用高分辨力的聚丙烯酰胺凝胶电泳分离、银染法显影技术,对云南省特有的白族、傣族、阿昌族、景颇族、德昂族、拉祜族、布朗族、哈尼族、普米族和基诺族等10个少数民族的F13A01、FESFPS和vWA3位点等位基因的基因频率分布进行了调查,获得了满意的结果,在不同群体中发现一些有意义的遗传差异。     

Red cell enzyme polymorphism in two populations of coastal Andhra Pradesh, South India

Four red cell enzyme polymorphisms: Esterase-D (ESD), Glyoxalase-I (GL01), Superoxide Dismutase (SOD) and Phosphoglucomutase (PGM1 and 2), have been studied in two endogamous populations (paidi and Valmiki) of North Coastal Andhra Pradesh, South India. Inter group comparison by chisquare analysis revealed no significant differences among them. An attempt was made to compare with those available for other populations from Andhra Pradesh.     

HUMTH01 allele distribution in four human samples. An interpopulation analysis

The analysis of STR HUMTH01 in four populations (Galicia, SE Spain, Morocco, Cape Verde) was carried out, with up to 8 alleles being found. The frequencies of these alleles determine values of heterozigosity ranging from 0,826 detected in Cape Verde to 0,778 in Morocco. A global comparison of world populations shows clear patterns of differentiation among the main human groups, both by way of the analysis of allele distribution profiles and by the application of a Correspondence Analysis. Caucasian populations are mainly characterised by the highest frequencies in allele 9.3, Mongoloids by a very high frequency of allele 9 and Negroids show the highest frequencies for allele 7 and mainly 8. A significant negative correlation (r=−0,916, p<0,001) found in the relationships between alleles 9 and 9.3 seems to suggest the participation of non-random evolutionary forces in the population dynamics of this marker.