The human butyrylcholinesterase (BChE) activity is less than 1% in the serum of silent variant individuals of Vysya community in India. They are homozygous for a point mutation at codon 307 (CTT → CCT) resulting in the substitution of leucine 307 by proline. The reason for the disappearance of the protein in the serum has not been explicated till date. Based on this background, we performed molecular dynamics simulation to probe the structural stability of Indian variant (L307P) in comparison with wild and other BChE variants (D70G, E497V, V142M) having differential esterase activity. The simulation of all the mutants except D70G showed a much larger Cα root mean square deviation from the wild BChE crystal structure, showing the overall conformational disturbance. Further analysis revealed that secondary structure of the mutant proteins was not stable. The orientation of the catalytic triad is also distorted in all the mutants. The distance between δ nitrogen of His438 to ε oxygen of Glu325 and ε nitrogen of His438 to γ oxygen of Ser198 were highly altered in L307P mutant than the wild and other three variants throughout the simulation. Such disparity of distances between the catalytic residues may be due to the change in the protein conformation attributing to their differential catalytic activity. Our studies thus prove that the Indian BChE L307P mutant with negligible activity is possibly due to its structural instability when compared to other BChE variants.

译文

在印度Vysya社区的沉默变异个体的血清中,人丁酰胆碱酯酶 (BChE) 活性低于1%。它们在密码子307 (CTT → CCT) 处的点突变是纯合的,导致亮氨酸307被脯氨酸取代。到目前为止,尚未阐明血清中蛋白质消失的原因。基于此背景,我们进行了分子动力学模拟,以探索印度变体 (L307P) 与野生和其他具有不同酯酶活性的BChE变体 (D70G,E497V,V142M) 的结构稳定性。除D70G外,所有突变体的模拟均显示出与野生BChE晶体结构相比更大的c α 均方根偏差,显示出总体构象干扰。进一步的分析表明,突变蛋白的二级结构不稳定。在所有突变体中,催化三联体的方向也会扭曲。在整个模拟过程中,在L307P突变体中,His438的 δ 氮与Glu325的 ε 氧之间的距离和His438的 ε 氮与Ser198的 γ 氧之间的距离变化很大。催化残基之间距离的这种差异可能是由于蛋白质构象的变化归因于其不同的催化活性。因此,我们的研究证明,与其他BChE变体相比,活性可忽略的印度BChE L307P突变体可能是由于其结构不稳定所致。

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