Institute of Biotechnology, National Taipei University of Technology, Taipei 10608, Taiwan.
J Biomol Struct Dyn. 2012;29(5):937-59. doi: 10.1080/07391102.2012.10507420.
The juvenile X-linked retinoschisis (XLRS) is a retinal disease caused by mutations in the secretory protein, retinoschisin (RS1). Majority of the disease is resulted from single point mutations on the RS1 discoidin domain with cysteine mutations being related to some of the more severe cases of XLRS. Previous studies have indicated that two mutations (C110Y and C219G), which involve cysteines that form intramolecular disulfide bonds in the native discoidin domain, resulted in different oligomerization states of the proteins and did not correlate with the degree of protein stability as calculated by the change in folding free energy. Through homology modeling, bioinformatics predictions, molecular dynamics (MD) and docking simulations, we attempt to investigate the effects of these two mutations on the structure of the RS1 discoidin domain in relevance to the discrepancy found between structural stability and aggregation propensity. Based on our findings, this discrepancy can be explained by the ability of C110Y mutant to establish suitable modules for initiating amorphous aggregation and to expand the aggregating mass through predominantly hydrophobic interactions. The low capability of C219G mutant to oligomerize, on the other hand, may be due to its greater structural instability and lesser hydrophobic tendency, two properties that may be unsupportive of aggregation. The results, altogether, indicate that aggregation propensity in the RS1 C110Y mutant is dependent upon the formation of suitable aggregating substrates for propagation of aggregation and not directly related to or determined by overall structural instability. As for the wildtype protein, the binding specificity of the spikes for biological function and the formation of octameric structure are contributed by important loop interactions, as well as evolved structural and sequence-based properties that prevent aggregation.
X 连锁青少年性视网膜劈裂症（XLRS）是一种由分泌蛋白视蛋白聚糖（RS1）突变引起的视网膜疾病。大多数疾病是由于 RS1 盘状结构域中的单个点突变引起的，其中半胱氨酸突变与 XLRS 的一些更严重病例有关。先前的研究表明，涉及在天然盘状结构域中形成分子内二硫键的半胱氨酸的两个突变（C110Y 和 C219G）导致蛋白质的不同寡聚状态，并且与由折叠自由能变化计算的蛋白质稳定性程度无关。通过同源建模、生物信息学预测、分子动力学（MD）和对接模拟，我们试图研究这两个突变对 RS1 盘状结构域结构的影响，与在结构稳定性和聚集倾向之间发现的差异有关。基于我们的发现，这种差异可以通过 C110Y 突变体建立适合起始无定形聚集的模块的能力来解释，并通过主要的疏水相互作用扩展聚集质量。另一方面，C219G 突变体的低寡聚能力可能是由于其结构不稳定性更大和疏水性较小，这两个特性可能不利于聚集。总之，结果表明，RS1 C110Y 突变体的聚集倾向取决于形成适合传播聚集的聚集底物，而不是直接与或由整体结构不稳定性决定。对于野生型蛋白，刺突的结合特异性对于生物功能和八聚体结构的形成是由重要的环相互作用以及防止聚集的进化结构和基于序列的特性贡献的。
