Entry mechanism used by a model retrovirus

性状（由申请方提供）：包膜病毒通过将其包膜直接融合至宿主细胞膜或在内化后融合至内体膜进入细胞。第一进入途径中的融合通过与同源受体结合来触发，而内吞途径中的融合通过内体内的低pH来引发。强有力的证据表明，逆转录病毒，禽肉瘤和白血病病毒（ASLV）的Env糖蛋白，使用受体结合和低pH值进入细胞：它经历了最初的构象变化，在质膜作为受体结合的结果，并在胞吞作用后，经历最终的变化诱导内体内的低pH值。这种双重触发机制的前所未有的利用允许ASLV Env的顺序重折叠，这导致融合比其他病毒更好地描绘。表达ASLV Env的细胞和表达同源受体的细胞之间融合的低pH要求已明确证明，但病毒进入期间对低pH的要求仍有争议。将使用脂质和内容物混合试验严格研究病毒-细胞和病毒-脂质体融合的pH依赖性。ASLV Env诱导融合的pH敏感性步骤的鉴别将通过停止融合的连续阶段并测试是否需要低pH值进行后续阶段来确定。对于许多不相关的病毒蛋白，一个共同的结构基序称为六螺旋束，已经出现;有令人信服的证据表明，这种结构是融合的关键。ASLV Env与其他已知结构的融合蛋白之间的序列同源性强烈表明其倾向于形成六螺旋束。ASLV Env是否折叠成束以促进融合将通过确定Env衍生的合成肽是否消除细胞-细胞融合来测试，如折叠成束的其他病毒蛋白的情况。阐明ASLV Env诱导融合的机制将有助于深入了解重要的人类病原体（如HIV、埃博拉病毒和流感病毒）进入细胞的基本原理，因此可以提出针对病毒病原体的新的抗病毒策略。

DESCRIPTION (provided by applicant): Enveloped viruses enter cells either by fusing their envelope directly to a host cell membrane or by fusing to endosomal membrane after being internalized. Fusion in the first entry pathway is triggered by binding to cognate receptor(s), whereas fusion in endocytotic pathway is initiated by low pH within the endosome. Strong evidence exists that the Env glycoprotein of the retrovirus, avian sarcoma and leukosis virus (ASLV), uses both receptor binding and low pH to enter the cell: it undergoes initial conformational changes at the plasma membrane as a result of receptor binding, and, after endocytosis, undergoes final changes induced by low pH within endosomes. The unprecedented utilization of this dual triggering mechanism allows the sequential refolding of the ASLV Env that leads to fusion to be better delineated than possible for other viruses. The low pH-requirement for fusion between cells expressing ASLV Env and cognate receptor-expressing cells has been unambiguously demonstrated, but the requirement for low pH during virus entry is still controversial. The pH-dependence of virus-cell and virus-liposome fusion will be rigorously investigated, using lipid and content mixing assays. The identity of the pH-sensitive steps of ASLV Env-induced fusion will be determined by arresting sequential stages of fusion and testing whether low pH is required to proceed to the subsequent stage. For many unrelated viral proteins, a common structural motif referred to as a six-helix bundle, has emerged; there is compelling evidence that this structure is critical for fusion. The sequence homology between ASLV Env and other fusion proteins with known structures strongly indicates its propensity to form a six-helix bundle. Whether ASLV Env does fold into a bundle to promote fusion will be tested by determining if Env-derived synthetic peptides abolish cell-cell fusion, as was the case for other viral proteins that fold into bundles. Delineating the mechanism of ASLV Env-induced fusion will provide insight into the basic principles by which important human pathogens, such as HIV, Ebola, and flu viruses enter cells and could therefore suggest new antiviral strategies against viral pathogens.