In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the re...In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the relationship between the experimental and simulation results were explored.Our computational findings on the secondary structure of SEB showed that at room temperature,the CD spectroscopic results were highly consistent with the MD results.Moreover,under heating conditions,the changing trends of helix,sheet and random coil obtained by CD spectral fitting were highly consistent with those obtained by MD.In order to gain a deeper understanding of the thermal stability mechanism of SEB,the MD trajectories were analyzed in terms of root mean square deviation(RMSD),secondary structure assignment(SSA),radius of gyration(R_(g)),free energy surfaces(FES),solvent-accessible surface area(SASA),hydrogen bonds and salt bridges.The results showed that at low heating temperature,domain Ⅰ without loops(omitting the mobile loop region)mainly relied on hydrophobic interaction to maintain its thermal stability,whereas the thermal stability of domain Ⅱ was mainly controlled by salt bridges and hydrogen bonds.Under high heating temperature conditions,the hydrophobic interactions in domain Ⅰ without loops were destroyed and the secondary structure was almost completely lost,while domain Ⅱ could still rely on salt bridges as molecular staples to barely maintain the stability of the secondary structure.These results help us to understand the thermodynamic and kinetic mechanisms that maintain the thermal stability of SEB at the molecular level,and provide a direction for establishing safer and more effective food sterilization processes.展开更多
Predictive microbiology was utilized to model Staphylococcus aureus （S. aureus） growth and staphylococcal enterotoxin A （SEA） production in milk in this study. The modifed logistic model, modifed Gompertz model an...Predictive microbiology was utilized to model Staphylococcus aureus （S. aureus） growth and staphylococcal enterotoxin A （SEA） production in milk in this study. The modifed logistic model, modifed Gompertz model and Baranyi model were applied to model growth data of S. aureus between 15℃ and 37℃. Model comparisons indicated that Baranyi model described the growth data more accurately than two others with a mean square error of 0.0129. Growth rates generated from Baranyi model matched the observed ones with a bias factor of 0.999 and an accuracy factor of 1.01, and ft a square root model with respect to temperature; other two modifed models both overestimated the observed ones. SEA amount began to be detected when the cell number reached106.4 cfu ？ mL-1, and showed the linear correlation with time. Besides, the rate of SEA production ftted an exponential relationship as a function of temperature. Predictions based on the study could be applied to indicate possible growth of S. aureus and prevent the occurrence of staphylococcal food poisoning.展开更多
目的:了解金黄色葡萄球菌肠毒素A(SEA)联合PML-RARα融合多肽体外诱导正常人外周血T细胞活化TCRζ链基因表达情况。方法:利用T细胞液体培养法分别与正常人外周血淋巴细胞加入PML-RARα融合多肽、SEA和SEA联合PML-RARα多肽诱导培养T细胞...目的:了解金黄色葡萄球菌肠毒素A(SEA)联合PML-RARα融合多肽体外诱导正常人外周血T细胞活化TCRζ链基因表达情况。方法:利用T细胞液体培养法分别与正常人外周血淋巴细胞加入PML-RARα融合多肽、SEA和SEA联合PML-RARα多肽诱导培养T细胞,其中SEA刺激包括培养初始或培养第5天加入SEA两组(PS、PSI),并设空白对照组(不加多肽及SEA)。分别收集各组培养20 d后细胞提取mRNA并合成cDNA,采用SYBR G reenⅠ荧光定量PCR和相对定量检测TCRζ链在不同组别T淋巴细胞中的表达情况,以β2微球蛋白基因(β2M)作为内参,根据相对定量公式:2-△△C t分析TCRζ链表达差异。结果:与空白组相比,联合诱导组在培养初始加入SEA及第5天加入SEA的培养T细胞中TCRζ链表达上升,而单独SEA诱导组的TCRζ链表达下降。结论:超抗原SEA联合PML-RARα多肽体外诱导T细胞可使TCRζ链基因表达水平升高,有望为研制急性早幼粒细胞白血病疫苗提供新的切入点。展开更多
文摘In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the relationship between the experimental and simulation results were explored.Our computational findings on the secondary structure of SEB showed that at room temperature,the CD spectroscopic results were highly consistent with the MD results.Moreover,under heating conditions,the changing trends of helix,sheet and random coil obtained by CD spectral fitting were highly consistent with those obtained by MD.In order to gain a deeper understanding of the thermal stability mechanism of SEB,the MD trajectories were analyzed in terms of root mean square deviation(RMSD),secondary structure assignment(SSA),radius of gyration(R_(g)),free energy surfaces(FES),solvent-accessible surface area(SASA),hydrogen bonds and salt bridges.The results showed that at low heating temperature,domain Ⅰ without loops(omitting the mobile loop region)mainly relied on hydrophobic interaction to maintain its thermal stability,whereas the thermal stability of domain Ⅱ was mainly controlled by salt bridges and hydrogen bonds.Under high heating temperature conditions,the hydrophobic interactions in domain Ⅰ without loops were destroyed and the secondary structure was almost completely lost,while domain Ⅱ could still rely on salt bridges as molecular staples to barely maintain the stability of the secondary structure.These results help us to understand the thermodynamic and kinetic mechanisms that maintain the thermal stability of SEB at the molecular level,and provide a direction for establishing safer and more effective food sterilization processes.
基金Supported by"Academic Backbone"Project of Northeast Agricultural University(15XG26)the National High-level Talents Special Support Program of China
文摘Predictive microbiology was utilized to model Staphylococcus aureus （S. aureus） growth and staphylococcal enterotoxin A （SEA） production in milk in this study. The modifed logistic model, modifed Gompertz model and Baranyi model were applied to model growth data of S. aureus between 15℃ and 37℃. Model comparisons indicated that Baranyi model described the growth data more accurately than two others with a mean square error of 0.0129. Growth rates generated from Baranyi model matched the observed ones with a bias factor of 0.999 and an accuracy factor of 1.01, and ft a square root model with respect to temperature; other two modifed models both overestimated the observed ones. SEA amount began to be detected when the cell number reached106.4 cfu ？ mL-1, and showed the linear correlation with time. Besides, the rate of SEA production ftted an exponential relationship as a function of temperature. Predictions based on the study could be applied to indicate possible growth of S. aureus and prevent the occurrence of staphylococcal food poisoning.
文摘目的:了解金黄色葡萄球菌肠毒素A(SEA)联合PML-RARα融合多肽体外诱导正常人外周血T细胞活化TCRζ链基因表达情况。方法:利用T细胞液体培养法分别与正常人外周血淋巴细胞加入PML-RARα融合多肽、SEA和SEA联合PML-RARα多肽诱导培养T细胞,其中SEA刺激包括培养初始或培养第5天加入SEA两组(PS、PSI),并设空白对照组(不加多肽及SEA)。分别收集各组培养20 d后细胞提取mRNA并合成cDNA,采用SYBR G reenⅠ荧光定量PCR和相对定量检测TCRζ链在不同组别T淋巴细胞中的表达情况,以β2微球蛋白基因(β2M)作为内参,根据相对定量公式:2-△△C t分析TCRζ链表达差异。结果:与空白组相比,联合诱导组在培养初始加入SEA及第5天加入SEA的培养T细胞中TCRζ链表达上升,而单独SEA诱导组的TCRζ链表达下降。结论:超抗原SEA联合PML-RARα多肽体外诱导T细胞可使TCRζ链基因表达水平升高,有望为研制急性早幼粒细胞白血病疫苗提供新的切入点。
