小柯机器人

低温STEM层析成像揭示铁蛋白结晶机制
2020-03-30 16:00

以色列魏茨曼科学研究所Boris Rybtchinski、Lothar Houben等研究人员合作,利用低温STEM层析成像揭示了铁蛋白结晶的机制。相关论文于2020年3月25日在线发表于国际学术期刊《自然》。

研究人员报道了,在结晶的各个阶段,铁蛋白聚集体的低温扫描透射显微镜层析成像,然后使用同时的迭代重建技术进行3D重建,以提供具有分子分辨率的3D结晶图片。随着聚集体中晶体顺序的逐渐增加,它们从表面到内部的顺序和密度均增加。
 
研究人员没有观察到经典成核过程中典型的高度有序的小结构,并且偶尔观察到在一个非晶态聚集体中出现了多个有序区,这种现象既不是经典成核理论也不是两步成核理论所预测的。这些分子水平的分析表明,去溶剂化是连续有序进化机制的驱动因素,这种观点超越了当前的成核模型,但与广泛的蛋白质结晶机制一致。
 
据悉,蛋白质结晶在结构生物学、疾病研究和药物中很重要。目前,人们已经意识到非经典结晶(涉及无定形前体相的初始形成)在蛋白质、有机和无机结晶过程频繁出现。因此,有研究人员提出了两步成核理论,即初始的低密度、溶剂化的无定形聚集体能够随后致密化,从而成核。
 
这种观点与经典的成核理论不同,经典的成核理论意味着溶液中形成的晶核具有与最终晶态相同的密度和结构。涉及这种经典途径的蛋白质结晶机制最近被直接观察到了。然而,非经典蛋白质结晶的分子机理尚未建立。为了确定无定形前体的性质以及是否在其中发生结晶(如果是,则在分子水平上如何先后发展),需要对结晶过程进行三维分子水平成像。
 
附:英文原文

Title: A mechanism of ferritin crystallization revealed by cryo-STEM tomography

Author: Lothar Houben, Haim Weissman, Sharon G. Wolf, Boris Rybtchinski

Issue&Volume: 2020-03-25

Abstract: Protein crystallization is important in structural biology, disease research and pharmaceuticals. It has recently been recognized that nonclassical crystallization—involving initial formation of an amorphous precursor phase—occurs often in protein, organic and inorganic crystallization processes1,2,3,4,5. A two-step nucleation theory has thus been proposed, in which initial low-density, solvated amorphous aggregates subsequently densify, leading to nucleation4,6,7. This view differs from classical nucleation theory, which implies that crystalline nuclei forming in solution have the same density and structure as does the final crystalline state1. A protein crystallization mechanism involving this classical pathway has recently been observed directly8. However, a molecular mechanism of nonclassical protein crystallization9,10,11,12,13,14,15 has not been established9,11,14. To determine the nature of the amorphous precursors and whether crystallization takes place within them (and if so, how order develops at the molecular level), three-dimensional (3D) molecular-level imaging of a crystallization process is required. Here we report cryogenic scanning transmission microscopy tomography of ferritin aggregates at various stages of crystallization, followed by 3D reconstruction using simultaneous iterative reconstruction techniques to provide a 3D picture of crystallization with molecular resolution. As crystalline order gradually increased in the studied aggregates, they exhibited an increase in both order and density from their surface towards their interior. We observed no highly ordered small structures typical of a classical nucleation process, and occasionally we observed several ordered domains emerging within one amorphous aggregate, a phenomenon not predicted by either classical or two-step nucleation theories. Our molecular-level analysis hints at desolvation as the driver of the continuous order-evolution mechanism, a view that goes beyond current nucleation models, yet is consistent with a broad spectrum of protein crystallization mechanisms.

DOI: 10.1038/s41586-020-2104-4

Source: https://www.nature.com/articles/s41586-020-2104-4

Nature:《自然》,创刊于1869年。隶属于施普林格·自然出版集团,最新IF:43.07
官方网址:http://www.nature.com/
投稿链接:http://www.nature.com/authors/submit_manuscript.html


本期文章:《自然》:Online/在线发表

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