Chen Bing, Vogan Erik M, Gong Haiyun, Skehel John J, Wiley Don C, Harrison Stephen C
Children's Hospital Laboratory of Molecular Medicine, Harvard Medical School, Boston, Massachusetts 02115, USA.
Structure. 2005 Feb;13(2):197-211. doi: 10.1016/j.str.2004.12.004.
HIV/SIV envelope glycoproteins mediate the first steps in viral infection. They are trimers of a membrane-anchored polypeptide chain, cleaved into two fragments known as gp120 and gp41. The structure of HIV gp120 bound with receptor (CD4) has been known for some time. We have now determined the structure of a fully glycosylated SIV gp120 envelope glycoprotein in an unliganded conformation by X-ray crystallography at 4.0 A resolution. We describe here our experimental and computational approaches, which may be relevant to other resolution-limited crystallographic problems. Key issues were attention to details of beam geometry mandated by small, weakly diffracting crystals, and choice of strategies for phase improvement, starting with two isomorphous derivatives and including multicrystal averaging. We validated the structure by analyzing composite omit maps, averaged among three distinct crystal lattices, and by calculating model-based, SeMet anomalous difference maps. There are at least four ordered sugars on many of the thirteen oligosaccharides.
HIV/SIV包膜糖蛋白介导病毒感染的起始步骤。它们是膜锚定多肽链的三聚体，裂解为两个片段，即gp120和gp41。HIV gp120与受体（CD4）结合的结构已为人所知有一段时间了。我们现在通过X射线晶体学以4.0埃分辨率确定了处于未结合配体构象的完全糖基化SIV gp120包膜糖蛋白的结构。我们在此描述我们的实验和计算方法，这些方法可能与其他受分辨率限制的晶体学问题相关。关键问题包括关注由小的、弱衍射晶体所要求的光束几何细节，以及从两个同晶型衍生物开始并包括多晶体平均的相位改善策略的选择。我们通过分析在三个不同晶格之间平均的复合省略图，并通过计算基于模型的硒代甲硫氨酸异常差异图来验证该结构。在13个寡糖中的许多寡糖上至少有4个有序糖。
