Molecular Microbiology and Structural Biochemistry Laboratory, CNRS UMR 5086, University of Lyon, IBCP, 7, passage du Vercors, 69367 Lyon, France.
Molecular Microbiology and Structural Biochemistry Laboratory, CNRS UMR 5086, University of Lyon, IBCP, 7, passage du Vercors, 69367 Lyon, France.
Biochim Biophys Acta Biomembr. 2023 Jan 1;1865(1):184065. doi: 10.1016/j.bbamem.2022.184065. Epub 2022 Oct 4.
Diffraction anisotropy is a phenomenon that impacts more specifically membrane proteins, compared to soluble ones, but the reasons for this discrepancy remained unclear. Often, it is referred to a difference in resolution limits between highest and lowest diffraction limits as a signature for anisotropy. We show in this article that there is no single correlation between anisotropy and difference in resolution limits, with notably a substantial number of structures displaying various anisotropy with no difference in resolution limits. We further investigated diffraction intensity profiles, and observed a peak centred on 4.9 Å resolution more predominant in membrane proteins. Since this peak is in the region corresponding to secondary structures, we investigated the influence of secondary structure ratio. We showed that secondary structure content has little influence on this profile, while secondary structure collinearity in membrane proteins correlate with a stronger peak. Finally, we could further show that the presence of this peak is linked to higher diffraction anisotropy. These results bring to light a specific diffraction of membrane protein crystals, which calls for a specific handling by crystallographic software. It also brings an explanation for investigators struggling with their anisotropic data.
各向异性是一种比可溶性蛋白更能影响膜蛋白的现象，但这种差异的原因仍不清楚。通常，人们将最高和最低衍射极限之间的分辨率极限差异称为各向异性的特征。在本文中，我们表明，各向异性和分辨率极限差异之间没有单一的相关性，许多结构表现出不同的各向异性，而分辨率极限没有差异。我们进一步研究了衍射强度分布，观察到一个中心位于 4.9 Å 分辨率的峰在膜蛋白中更为突出。由于这个峰位于对应于二级结构的区域，我们研究了二级结构比例的影响。我们表明，二级结构含量对这个分布的影响很小，而膜蛋白中二级结构的共线性与更强的峰相关。最后，我们可以进一步表明，这个峰的存在与更高的衍射各向异性有关。这些结果揭示了膜蛋白晶体的一种特殊衍射，这需要晶体学软件的特殊处理。它也为那些正在处理各向异性数据的研究人员提供了一个解释。
