Elucidation of HIV-1 envelope incorporation into virions

我们和其他人提出了人类免疫缺陷病毒1型(HIV-1)Gag蛋白的基质(MA)结构域与跨膜包膜(Env)糖蛋白gp41的细胞质尾部之间直接相互作用的证据。此外，推测GAG的MA结构域在GAG处理后发生了构象变化，并且gp41的细胞质尾部被证明调节了Env介导的膜融合活性。综上所述，这些结果提出了gp41细胞质尾巴与MA之间的相互作用受蛋白酶(PR)介导的GAG处理调控的可能性，可能影响Env的功能。为了检验Gag处理是否影响Env介导的融合，我们比较了WT HIV-1Env和一个缺乏gp41细胞质尾巴的突变体在活跃(PR^)或非活跃(PR^-)病毒PR的背景下诱导融合的能力。我们观察到携带WT Env的PR^-病毒粒子在细胞-细胞融合中表现出缺陷。融合受损并不是由于病毒粒子相关的Env水平的差异，也不是由于CD4依赖的与靶细胞的结合，或者CD4诱导的gp41六螺旋束的形成。有趣的是，gp41胞浆尾巴的截断逆转了融合缺陷。这些结果表明，未处理的GAG与gp41细胞质Tail之间的相互作用抑制了融合。

We and others have presented evidence for a direct interaction between the matrix(MA) domain of the human immunodeficiency virus type 1(HIV-1) Gag protein and the cytoplasmic tail of the transmembrane envelope(Env) glycoprotein gp41. In addition, it has been postulated that the MA domain of Gag undergoes a conformational change following Gag processing and the cytoplasmic tail of gp41 has been shown to modulate Env-mediated membrane fusion activity. Together, these results raise the possibility that the interaction between the gp41 cytoplasmic tail and MA is regulated by protease(PR)-mediated Gag processing, perhaps affecting Env function. To examine whether Gag processing affects Env-mediated fusion, we compared the ability of WT HIV-1 Env and a mutant lacking the gp41 cytoplasmic tail to induce fusion in the context of an active(PR^+) or inactive(PR^-) viral PR. We observed that PR^-virions bearing WT Env displayed defects in cell-cell fusion. Impaired fusion did not pear to be due to differences in the levels of virion-associated Env, in CD4-dependent binding to target cells, or in the formation of the CD4-induced gp41 six-helix bundle. Interestingly, truncation of the gp41 cytoplasmic tail reversed the fusion defect. These results suggest that interactions between unprocessed Gag and the gp41 cytoplasmic tail suppress fusion.