The entry mechanism used by a model retrovirus.

描述(申请人提供)：被包裹的病毒通过将其包膜直接融合到宿主细胞膜或在内化后融合到内体膜而进入细胞。第一个进入途径的融合是由与同源受体(S)结合而触发的，而内吞途径的融合是由内吞体内的低pH启动的。有强有力的证据表明，逆转录病毒、禽肉瘤和白血病病毒(ASLV)的Env糖蛋白利用受体结合和低pH进入细胞：由于受体结合，它在质膜上经历最初的构象变化，并在内吞后，经历内吞体内低pH诱导的最终变化。这种双重触发机制的史无前例的利用使得导致融合的ASLV Env的顺序重折叠比其他病毒更好地被描绘出来。表达ASLV Env的细胞和表达同源受体的细胞之间的融合对低pH的要求已经被明确地证明了，但在病毒进入时对低pH的要求仍然存在争议。将严格研究病毒-细胞和病毒-脂质体融合的pH依赖性，使用脂类和内容物混合分析。ASLV Env诱导的融合的pH敏感步骤的一致性将通过阻止融合的连续阶段和测试是否需要低pH值进行到下一阶段来确定。对于许多无关的病毒蛋白，一种被称为六螺旋束的常见结构基序已经出现；有令人信服的证据表明，这种结构对融合至关重要。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它有形成六螺旋束的倾向。ASLV Env是否折叠成束以促进融合将通过确定Env衍生的合成肽是否像其他折叠成束的病毒蛋白那样取消细胞-细胞融合来测试。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、埃博拉和流感病毒进入细胞的基本原理，从而可能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.