Envelope proteins containing single amino acid substitutions support a structural model of the receptor-binding domain of bovine leukemia virus surface protein
Envelope proteins containing single amino acid substitutions support a structural model of the receptor-binding domain of bovine leukemia virus surface protein
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DOI：
10.1128/jvi.76.21.10861-10872.2002
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发表时间：
2002-11-01
影响因子：
5.4
通讯作者：
Radke, K
中科院分区：
文献类型：
--
作者：
Johnston, ER;Albritton, LM;Radke, K
牛白血病病毒（BLV）及其近亲人T细胞白血病病毒1型（HTLV-1）的显著保守的包膜（Env）糖蛋白的功能结构域仍在定义中。我们已经使用BLV Env蛋白变体来深入了解病毒感染性的这一重要决定因素的结构和功能。在BLV感染的绵羊外周血单核细胞短期培养后存在的env转录物的cDNA克隆中发现的23种不同的单一氨基酸变体中的每一种在COS-1细胞中表达，并测试介导细胞融合和切割成表面（SU）和跨膜（TM）蛋白亚基的能力。在11种不能诱导合胞体或诱导效果很差的Env变体中，有7种含有与HTLV-1 Env蛋白相同或化学保守的氨基酸变化。这七个包括显示异常蛋白水解切割和差的细胞表面表达的四个变体，强调了它们对Env结构的重要性。12个保留野生型合胞体诱导能力的变体中有10个聚集在BLV SU的N末端一半，形成了推定的受体结合结构域（RBD）。RBD中的几个变体显示出细微错误折叠的证据，如通过与识别由SU的N末端形成的构象表位F、G和H的单克隆抗体的结合减少所判断的。我们通过将推定的结构元件与亲嗜性Friend鼠白血病病毒RBD单体的已知元件对齐来模拟BLV RBD。除了一个之外的所有变体RBD残基都暴露在该BLV模型的表面上。这些变体以及其他研究者定义的改变功能的抗体反应性残基在分子模型的一个面上。它们在相反的面上明显缺席，这意味着它可能在Env复合物中面向内。该表面可能与SU的C-末端结构域或与Env寡聚体中的相邻单体相互作用。该位置表明亲嗜性Friend鼠白血病病毒RBD的单体的取向。
Functional domains of the strikingly conserved envelope (Env) glycoproteins of bovine leukemia virus (BLV) and its close relative, human T-cell leukemia virus type 1 (HTLV-1), are still being defined. We have used BLV Env protein variants to gain insights into the structure and function of this important determinant of viral infectivity. Each of 23 different single amino acid variants found in cDNA clones of env transcripts present after short-term culture of peripheral blood mononuclear cells from BLV-infected sheep was expressed in COS-1 cells and tested for the ability to mediate cell fusion and to be cleaved to surface (SU) and transmembrane (TM) protein subunits. Of 11 Env variants that failed to induce syncytia or did so poorly, 7 contained changes in amino acids identical or chemically conserved in the HTLV-1 Env protein. These seven included the four variants that showed aberrant proteolytic cleavage and poor cell surface expression, underscoring their importance for Env structure. Ten of 12 variants that retained wild-type syncytium-inducing ability clustered in the N-terminal half of BLV SU, which forms the putative receptor-binding domain (RBD). Several variants in the RBD showed evidence of subtle misfolding, as judged by reduced binding to monoclonal antibodies recognizing conformational epitopes F, G, and H formed by the N terminus of SU. We modeled the BLV RBD by aligning putative structural elements with known elements of the ecotropic Friend murine leukemia virus RBD monomer. All the variant RBD residues but one are exposed on the surface of this BLV model. These variants as well as function-altering, antibody-reactive residues defined by other investigators group on one face of the molecular model. They are strikingly absent from the opposite face, implying that it is likely to face inward in Env complexes. This surface might interact with the C-terminal domain of SU or with an adjacent monomer in the Env oligomer. This location suggests an orientation for the monomer of ecotropic Friend murine leukemia virus RBD.