Hall Zoe, Schmidt Carla, Politis Argyris
From the Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, United Kingdom, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom, and.
Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom, and.
J Biol Chem. 2016 Feb 26;291(9):4626-37. doi: 10.1074/jbc.M115.691063. Epub 2015 Dec 10.
β2-Microglobulin (β2m), a key component of the major histocompatibility class I complex, can aggregate into fibrils with severe clinical consequences. As such, investigating the structural aspects of the formation of oligomeric intermediates of β2m and their subsequent progression toward fibrillar aggregates is of great importance. However, β2m aggregates are challenging targets in structural biology, primarily due to their inherent transient and heterogeneous nature. Here we study the oligomeric distributions and structures of the early intermediates of amyloidogenic β2m and its truncated variant ΔN6-β2m. We established compact oligomers for both variants by integrating advanced mass spectrometric techniques with available electron microscopy maps and atomic level structures from NMR spectroscopy and x-ray crystallography. Our results revealed a stepwise assembly mechanism by monomer addition and domain swapping for the oligomeric species of ΔN6-β2m. The observed structural similarity and common oligomerization pathway between the two variants is likely to enable ΔN6-β2m to cross-seed β2m fibrillation and allow the formation of mixed fibrils. We further determined the key subunit interactions in ΔN6-β2m tetramer, revealing the importance of a domain-swapped hinge region for formation of higher order oligomers. Overall, we deliver new mechanistic insights into β2m aggregation, paving the way for future studies on the mechanisms and cause of amyloid fibrillation.
β2微球蛋白（β2m）是主要组织相容性复合体I类的关键组成部分，可聚集成纤维，产生严重的临床后果。因此，研究β2m寡聚中间体形成的结构方面及其随后向纤维状聚集体的进展非常重要。然而，β2m聚集体是结构生物学中的挑战性目标，主要是由于其固有的瞬态和异质性。在这里，我们研究了淀粉样β2m及其截短变体ΔN6-β2m早期中间体的寡聚分布和结构。我们通过将先进的质谱技术与现有的电子显微镜图谱以及核磁共振光谱和X射线晶体学的原子水平结构相结合，为这两种变体建立了紧密的寡聚体。我们的结果揭示了ΔN6-β2m寡聚体通过单体添加和结构域交换的逐步组装机制。观察到的两种变体之间的结构相似性和共同的寡聚化途径可能使ΔN6-β2m能够交叉引发β2m纤维化并允许形成混合纤维。我们进一步确定了ΔN6-β2m四聚体中的关键亚基相互作用，揭示了结构域交换铰链区域对形成高阶寡聚体的重要性。总体而言，我们为β2m聚集提供了新的机制见解，为未来关于淀粉样纤维化机制和原因的研究铺平了道路。
