Qin Haina, Lim Liangzhong, Wei Yuanyuan, Gupta Garvita, Song Jianxing
Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, 119260, Singapore.
NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, 119260, Singapore.
F1000Res. 2013 Oct 21;2:221. doi: 10.12688/f1000research.2-221.v2. eCollection 2013.
Paradoxically, aggregation of specific proteins is characteristic of many human diseases and aging, yet aggregates have increasingly been found to be unnecessary for initiating pathogenesis. Here we determined the NMR topology and dynamics of a helical mutant in a membrane environment transformed from the 125-residue cytosolic all-β MSP domain of vesicle-associated membrane protein-associated protein B (VAPB) by the ALS-causing P56S mutation. Despite its low hydrophobicity, the P56S major sperm protein (MSP) domain becomes largely embedded in the membrane environment with high backbone rigidity. Furthermore it is composed of five helices with amphiphilicity comparable to those of the partly-soluble membrane toxin mellitin and α-synuclein causing Parkinson's disease. Consequently, the mechanism underlying this chameleon transformation becomes clear: by disrupting the specific tertiary interaction network stabilizing the native all-β MSP fold to release previously-locked amphiphilic segments, the P56S mutation acts to convert the classic MSP fold into a membrane-active protein that is fundamentally indistinguishable from mellitin and α-synuclein which are disordered in aqueous solution but spontaneously partition into membrane interfaces driven by hydrogen-bond energetics gained from forming α-helix in the membrane environments. As segments with high amphiphilicity exist in all proteins, our study successfully resolves the paradox by deciphering that the proteins with a higher tendency to aggregate have a stronger potential to partition into membranes through the same mechanism as α-synuclein to initially attack membranes to trigger pathogenesis without needing aggregates. This might represent the common first step for various kinds of aggregated proteins to trigger familiar, sporadic and aging diseases. Therefore the homeostasis of aggregated proteins in vivo is the central factor responsible for a variety of human diseases including aging. The number and degree of the membrane attacks by aggregated proteins may act as an endogenous clock to count down the aging process. Consequently, a key approach to fight against them is to develop strategies and agents to maintain or even enhance the functions of the degradation machineries.
矛盾的是，特定蛋白质的聚集是许多人类疾病和衰老的特征，但越来越多的研究发现，聚集物对于引发发病机制并非必要。在这里，我们通过导致肌萎缩侧索硬化症（ALS）的P56S突变，确定了从囊泡相关膜蛋白相关蛋白B（VAPB）的125个残基胞质全β MSP结构域转化而来的螺旋突变体在膜环境中的核磁共振（NMR）拓扑结构和动力学。尽管其疏水性较低，但P56S主要精子蛋白（MSP）结构域在膜环境中大部分嵌入，且具有高主链刚性。此外，它由五个螺旋组成，其两亲性与部分可溶的膜毒素蜂毒素和导致帕金森病的α-突触核蛋白相当。因此，这种变色龙式转变的潜在机制变得清晰：通过破坏稳定天然全β MSP折叠的特定三级相互作用网络，释放先前锁定的两亲性片段，P56S突变将经典的MSP折叠转化为一种膜活性蛋白，该蛋白与蜂毒素和α-突触核蛋白在本质上没有区别，后者在水溶液中无序，但在膜环境中通过形成α-螺旋获得的氢键能量驱动下自发分配到膜界面。由于所有蛋白质中都存在具有高两亲性的片段，我们的研究通过破译具有更高聚集倾向的蛋白质具有更强的通过与α-突触核蛋白相同的机制分配到膜中的潜力，从而成功解决了这一矛盾，即无需聚集物即可最初攻击膜以触发发病机制。这可能代表了各种聚集蛋白引发常见、散发性和衰老疾病的共同第一步。因此，体内聚集蛋白的稳态是导致包括衰老在内的各种人类疾病的核心因素。聚集蛋白对膜的攻击次数和程度可能作为一个内源性时钟来倒计时衰老过程。因此，对抗它们的关键方法是开发策略和药物来维持甚至增强降解机制的功能。
