钙离子和钠离子协同改善直链麦芽低聚糖生成酶的热稳定性
首发时间:2017-11-14
摘要:本论文主要研究了来源于嗜热脂肪芽孢杆菌STB04的直链麦芽低聚糖生成酶(Bst-MFA)的热稳定性,重点探究了钙离子和钠离子对其热稳定性的影响。结果显示,无离子添加时,Bst-MFA在80 C下保温5 min后基本失去活力,添加终浓度为10 mM的钙离子后可使该酶在80 C下的半衰期延长至82.5 min;钙离子和钠离子对Bst-MFA热稳定性的提高存在协同作用,在添加终浓度10 mM钙离子的基础上,再添加40 mM的钠离子可使Bst-MFA的热稳定性进一步提高,在80 C下保温180 min后仍可保留71.1%的残余酶活。通过SWISS-MODEL分子结构模拟、远紫外圆二色谱、内源荧光色谱等手段,从酶蛋白分子结构的角度分析了钙、钠离子协同改善酶热稳定性的机理。研究发现,在Bst-MFA的三级结构中存在着一个重要的钙-钠-钙三联体结合位点,当环境中同时存在这两种离子时,可有效维持酶二级结构正确有序的折叠,并提高三级结构的稳定性。
关键词: 直链麦芽低聚糖生成酶 热稳定性 协同作用 钙-钠-钙三联体
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Ca2+ and Na+ synergistically improve the thermostability of a maltooligosaccharide-forming amylase
Abstract:In this paperthe thermostability of a maltooligosaccharide-forming amylase from Bacillus stearothermophilus STB04(Bst-MFA)wasinvestigated. Particularly,the effect of calcium ion and sodium ion on its thermostability was determined. The results showed thatBst-MFA almost totally lost activity after 5 min of incubation at 80 C without ions. While 10 mM sodium ionextended the half-life of Bst-MFA at 80 C to 82.5 min; further study suggested that calcium ion and sodium ion could synergistically improve the thermostability of Bst-MFA: incubated with 10 mM calcium ionand 40 mM sodium ion at 80 C for 180 min, the residual activity of Bst-MFA could dramaticallyretain 71.1%. The mechanism of this synergistic effect was illuminated by SWISS-MODEL protein modelling, far-UV circular dichroism and intrinsic fluorescence spectra. The results indicated that there was an important calcium - sodium - calcium triad in the structure of Bst-MFA.When these two ions existed, the calcium - sodium - calcium triad could effectively maintain the correct and ordered folding of the secondary structureof Bst-MFAand improve the stablity of tertiary structure.
Keywords: maltooligosaccharide-forming amylase thermostability synergistic effect calcium - sodium - calcium triad
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钙离子和钠离子协同改善直链麦芽低聚糖生成酶的热稳定性
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