Receptors and Entry Cofactors for Retroviruses Include Single and Multiple Transmembrane-Spanning Proteins as well as Newly Described Glycophosphatidylinositol-Anchored and Secreted Proteins

In the past few years, many retrovirus receptors, coreceptors, and cofactors have been identified. These molecules are important for some aspects of viral entry, although in some cases it remains to be determined whether they are required for binding or postbinding stages in entry, such as fusion. There are certain common features to the molecules that many retroviruses use to gain entry into the cell. For example, the receptors for most mammalian oncoretroviruses are multiple membrane-spanning transport proteins. However, avian retroviruses use single-pass membrane proteins, and a sheep retrovirus uses a glycosylphosphatidylinositol-anchored molecule as its receptor. For some retroviruses, particularly the lentiviruses, two cell surface molecules are required for efficient entry. More recently, a soluble protein that is required for viral entry has been identified for a feline oncoretrovirus. In this review, we will focus on the various strategies used by mammalian retroviruses to gain entry into the cell. The choice of receptors will also be discussed in light of pressures that drive viral evolution and persistence.

近数十年来，诸多逆转录病毒（retrovirus）受体、共受体及辅助因子已被成功鉴定。这些分子对于病毒入侵的多个环节至关重要，但在部分场景中，尚需明确其究竟是参与病毒结合步骤，还是作用于入侵过程中结合后的阶段（如膜融合）。多数逆转录病毒用以入侵宿主细胞的受体分子，存在若干共通特征。例如，多数哺乳类肿瘤逆转录病毒（oncoretrovirus）的受体为多次跨膜转运蛋白。然而，禽类逆转录病毒则采用单次跨膜蛋白作为受体，而某绵羊逆转录病毒的受体为糖基磷脂酰肌醇（glycosylphosphatidylinositol）锚定分子。对于部分逆转录病毒（尤其是慢病毒（lentivirus））而言，需两种细胞表面分子方可实现高效入侵。近期，研究人员已针对某猫科肿瘤逆转录病毒，鉴定出一种对其入侵必不可少的可溶性蛋白。本综述将聚焦哺乳类逆转录病毒入侵宿主细胞的各类策略。同时，本文还将结合驱动病毒进化与存续的选择压力，探讨病毒对受体的选择机制。