Torres Jaume, Parthasarathy Krupakar, Lin Xin, Saravanan Rathi, Kukol Andreas, Liu Ding Xiang
School of Biological Sciences, Nanyang Technological University, Singapore.
Biophys J. 2006 Aug 1;91(3):938-47. doi: 10.1529/biophysj.105.080119. Epub 2006 May 12.
The coronavirus responsible for the severe acute respiratory syndrome contains a small envelope protein, E, with putative involvement in host apoptosis and virus morphogenesis. To perform these functions, it has been suggested that protein E can form a membrane destabilizing transmembrane (TM) hairpin, or homooligomerize to form a TM pore. Indeed, in a recent study we reported that the alpha-helical putative transmembrane domain of E protein (ETM) forms several SDS-resistant TM interactions: a dimer, a trimer, and two pentameric forms. Further, these interactions were found to be evolutionarily conserved. Herein, we have studied multiple isotopically labeled ETM peptides reconstituted in model lipid bilayers, using the orientational parameters derived from infrared dichroic data. We show that the topology of ETM is consistent with a regular TM alpha-helix. Further, the orientational parameters obtained unequivocally correspond to a homopentameric model, by comparison with previous predictions. We have independently confirmed that the full polypeptide of E protein can also aggregate as pentamers after expression in Escherichia coli. This interaction must be stabilized, at least partially, at the TM domain. The model we report for this pentameric alpha-helical bundle may explain some of the permabilizing properties of protein E, and should be the basis of mutagenesis efforts in future functional studies.
导致严重急性呼吸综合征的冠状病毒含有一种小的包膜蛋白E，推测其参与宿主细胞凋亡和病毒形态发生。为了执行这些功能，有人提出蛋白E可以形成破坏膜稳定性的跨膜（TM）发夹结构，或形成同型寡聚体以形成TM孔。事实上，在最近的一项研究中，我们报道E蛋白的α螺旋推定跨膜结构域（ETM）形成了几种抗SDS的TM相互作用：二聚体、三聚体和两种五聚体形式。此外，发现这些相互作用在进化上是保守的。在此，我们使用从红外二色性数据得出的取向参数，研究了在模型脂质双层中重构的多个同位素标记的ETM肽。我们表明ETM的拓扑结构与规则的TMα螺旋一致。此外，通过与先前的预测进行比较，获得的取向参数明确对应于同型五聚体模型。我们独立证实，E蛋白的完整多肽在大肠杆菌中表达后也可以聚合成五聚体。这种相互作用必须至少部分地在TM结构域处稳定。我们报道的这种五聚体α螺旋束模型可能解释了蛋白E的一些通透性质，并且应该是未来功能研究中诱变努力的基础。
