Watts Norman R, Conway James F, Cheng Naiqian, Stahl Stephen J, Belnap David M, Steven Alasdair C, Wingfield Paul T
Protein Expression Laboratory, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Building 50, Room 1517, 50 South drive MSC 8025, National Institutes of Health, Bethesda, MD 20892-8025, USA.
EMBO J. 2002 Mar 1;21(5):876-84. doi: 10.1093/emboj/21.5.876.
Many capsid proteins have peptides that influence their assembly. In hepatitis B virus capsid protein, the peptide STLPETTVV, linking the shell-forming 'core' domain and the nucleic acid-binding 'protamine' domain, has such a role. We have studied its morphogenic properties by permuting its sequence, substituting it with an extraneous peptide, deleting it to directly fuse the core and protamine domains and assembling core domain dimers with added linker peptides. The peptide was found to be necessary for the assembly of protamine domain-containing capsids, although its size-determining effect tolerates some modifications. Although largely invisible in a capsid crystal structure, we could visualize linker peptides by cryo-EM difference imaging: they emerge on the inner surface and extend from the capsid protein dimer interface towards the adjacent symmetry axis. A closely sequence-similar peptide in cellobiose dehydrogenase, which has an extended conformation, offers a plausible prototype. We propose that linker peptides are attached to the capsid inner surface as hinged struts, forming a mobile array, an arrangement with implications for morphogenesis and the management of encapsidated nucleic acid.
许多衣壳蛋白含有影响其组装的肽段。在乙肝病毒衣壳蛋白中，连接形成外壳的“核心”结构域和核酸结合“鱼精蛋白”结构域的肽段STLPETTVV就具有这样的作用。我们通过置换其序列、用外源肽段替换它、删除它以直接融合核心结构域和鱼精蛋白结构域以及用添加的连接肽组装核心结构域二聚体，研究了其形态发生特性。发现该肽段对于含鱼精蛋白结构域的衣壳组装是必需的，尽管其大小决定作用能耐受一些修饰。虽然在衣壳晶体结构中基本上不可见，但我们可以通过冷冻电镜差异成像观察到连接肽：它们出现在内表面，从衣壳蛋白二聚体界面延伸至相邻对称轴。纤维二糖脱氢酶中一个序列相似且具有延伸构象的肽段提供了一个合理的原型。我们提出连接肽作为铰链支柱附着在衣壳内表面，形成一个可移动的阵列，这种排列对形态发生和包裹核酸的管理具有重要意义。
