State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin 300071, China.
Retrovirology. 2014 Mar 21;11:26. doi: 10.1186/1742-4690-11-26.
The equine infectious anemia virus (EIAV) is a lentivirus of the Retrovirus family, which causes persistent infection in horses often characterized by recurrent episodes of high fever. It has a similar morphology and life cycle to the human immunodeficiency virus (HIV). Its transmembrane glycoprotein, gp45 (analogous to gp41 in HIV), mediates membrane fusion during the infection. However, the post-fusion conformation of EIAV gp45 has not yet been determined. EIAV is the first member of the lentiviruses for which an effective vaccine has been successfully developed. The attenuated vaccine strain, FDDV, has been produced from a pathogenic strain by a series of passages in donkey dermal cells. We have previously reported that a V/I505T mutation in gp45, in combination with other mutations in gp90, may potentially contribute to the success of the vaccine strain. To this end, we now report on our structural and biochemical studies of the gp45 protein from both wide type and vaccine strain, providing a valuable structural model for the advancement of the EIAV vaccine.
We resolved crystal structures of the ecto-domain of gp45 from both the wild-type EIAV and the vaccine strain FDDV. We found that the V/I505T mutation in gp45 was located in a highly conserved d position within the heptad repeat, which protruded into a 3-fold symmetry axis within the six-helix bundle. Our crystal structure analyses revealed a shift of a hydrophobic to hydrophilic interaction due to this specific mutation, and further biochemical and virological studies confirmed that the mutation reduced the overall stability of the six-helix bundle in post-fusion conformation. Moreover, we found that altering the temperatures drastically affected the viral infectivity.
Our high-resolution crystal structures of gp45 exhibited high conservation between the gp45/gp41 structures of lentiviruses. In addition, a hydrophobic to hydrophilic interaction change in the EIAV vaccine strain was found to modulate the stability and thermal-sensitivity of the overall gp45 structure. Our observations suggest that lowering the stability of the six-helix bundle (post-fusion), which may stabilizes the pre-fusion conformation, might be one of the reasons of acquired dominance for FDDV in viral attenuation.
马传染性贫血病毒（EIAV）是逆转录病毒科的慢病毒，可导致马的持续性感染，通常表现为反复发作的高热。它的形态和生命周期与人类免疫缺陷病毒（HIV）相似。其跨膜糖蛋白 gp45（与 HIV 中的 gp41 类似）在感染过程中介导膜融合。然而，EIAV gp45 的融合后构象尚未确定。EIAV 是第一种成功开发出有效疫苗的慢病毒。减毒疫苗株 FDDV 是通过在驴皮肤细胞中进行一系列传代从致病性毒株中产生的。我们之前报道过，gp45 中的 V/I505T 突变与 gp90 中的其他突变相结合，可能有助于疫苗株的成功。为此，我们现在报告了对来自野生型和疫苗株的 gp45 蛋白的结构和生化研究，为 EIAV 疫苗的发展提供了有价值的结构模型。
我们解析了来自野生型 EIAV 和疫苗株 FDDV 的 gp45 外显子结构的晶体结构。我们发现，gp45 中的 V/I505T 突变位于七肽重复中的高度保守的 d 位，该突变突出到六螺旋束的 3 倍对称轴内。我们的晶体结构分析显示，由于这种特定突变，疏水相互作用转变为亲水相互作用，进一步的生化和病毒学研究证实，该突变降低了融合后构象中六螺旋束的整体稳定性。此外，我们发现改变温度会极大地影响病毒的感染力。
我们的 gp45 高分辨率晶体结构显示了慢病毒的 gp45/gp41 结构之间的高度保守性。此外，在 EIAV 疫苗株中发现的疏水到亲水相互作用的变化调节了整个 gp45 结构的稳定性和热敏感性。我们的观察结果表明，降低六螺旋束（融合后）的稳定性，可能稳定融合前构象，这可能是 FDDV 在病毒减毒中获得优势的原因之一。
