Hassan Mubashir, Abbas Qamar, Raza Hussain, Moustafa Ahmed A, Seo Sung-Yum
Department of Biological Sciences, College of Natural Sciences, Kongju National University, 56 Gongjudehak-Ro 56, Gongju, Chungnam 32588, Republic of Korea.
School of Social Sciences and Psychology, Western Sydney University, Sydney, New South Wales, Australia and MARCS Institute for Brain and Behaviour, Western Sydney University, Sydney, New South Wales, Australia.
Mol Biosyst. 2017 Jul 25;13(8):1534-1544. doi: 10.1039/c7mb00211d.
Misfolding and structural alteration in proteins lead to serious malfunctions and cause various diseases in humans. Mutations at the active binding site in tyrosinase impair structural stability and cause lethal albinism by abolishing copper binding. To evaluate the histidine mutational effect, all mutated structures were built using homology modelling. The protein sequence was retrieved from the UniProt database, and 3D models of original and mutated human tyrosinase sequences were predicted by changing the residual positions within the target sequence separately. Structural and mutational analyses were performed to interpret the significance of mutated residues (N, R, Q, R, Y, R, Y and D) at the active binding site of tyrosinases. CSpritz analysis depicted that 23.25% residues actively participate in the instability of tyrosinase. The accuracy of predicted models was confirmed through online servers ProSA-web, ERRAT score and VERIFY 3D values. The theoretical pI and GRAVY generated results also showed the accuracy of the predicted models. The CCA negative correlation results depicted that the replacement of mutated residues at His within the active binding site disturbs the structural stability of tyrosinases. The predicted CCA scores of Tyr (-0.079) and Q/R (0.032) revealed that both mutations have more potential to disturb the structural stability. MD simulation analyses of all predicted models justified that Gln, Arg, Tyr and D replacement made the protein structures more susceptible to destabilization. Mutational results showed that the replacement of His with Q/R and Y/R has a lethal effect and may cause melanin associated diseases such as OCA1. Taken together, our computational analysis depicts that the mutated residues such as Q/R and Y/R actively participate in instability and misfolding of tyrosinases, which may govern OCA1 through disturbing the melanin biosynthetic pathway.
蛋白质的错误折叠和结构改变会导致严重的功能故障，并引发人类的各种疾病。酪氨酸酶活性结合位点的突变会损害结构稳定性，并通过消除铜结合导致致死性白化病。为了评估组氨酸突变的影响，所有突变结构均使用同源建模构建。从UniProt数据库中检索蛋白质序列，并通过分别改变目标序列内的残基位置来预测原始和突变的人类酪氨酸酶序列的三维模型。进行了结构和突变分析，以解释酪氨酸酶活性结合位点处突变残基（N、R、Q、R、Y、R、Y和D）的意义。CSpritz分析表明，23.25%的残基积极参与酪氨酸酶的不稳定性。通过在线服务器ProSA-web、ERRAT评分和VERIFY 3D值确认了预测模型的准确性。理论pI和GRAVY生成的结果也显示了预测模型的准确性。CCA负相关结果表明，活性结合位点处组氨酸突变残基的替换会干扰酪氨酸酶的结构稳定性。酪氨酸（-0.079）和Q/R（0.032）的预测CCA分数表明，这两种突变都更有可能干扰结构稳定性。所有预测模型的分子动力学模拟分析证明，谷氨酰胺、精氨酸、酪氨酸和天冬氨酸的替换使蛋白质结构更容易不稳定。突变结果表明，用Q/R和Y/R替换组氨酸具有致死作用，可能导致与黑色素相关的疾病，如眼皮肤白化病1型。综上所述，我们的计算分析表明，Q/R和Y/R等突变残基积极参与酪氨酸酶的不稳定性和错误折叠，这可能通过干扰黑色素生物合成途径来控制眼皮肤白化病1型。
