Determinants Flanking the CD4 Binding Loop Modulate Macrophage Tropism of Human Immunodeficiency Virus Type 1 R5 Envelopes
Determinants Flanking the CD4 Binding Loop Modulate Macrophage Tropism of Human Immunodeficiency Virus Type 1 R5 Envelopes
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DOI：
10.1128/jvi.02133-08
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发表时间：
2009-03-15
影响因子：
5.4
通讯作者：
Clapham, Paul R.
中科院分区：
文献类型：
--
作者：
Duenas-Decamp, Maria Jose;Peters, Paul J.;Clapham, Paul R.
人类免疫缺陷病毒 1 型 R5 病毒的表型差异很大。因此，患有神经系统并发症的个体脑组织中的 R5 包膜 (env) 通常具有高度巨噬细胞嗜性。巨噬细胞的趋向性与包膜利用低 CD4 水平进行感染的能力相关。此外，CD4 结合位点内残基 283 处天冬酰胺的存在与脑源性包膜、env-CD4 亲和力增加和巨噬细胞向性增强有关。在这里，我们确定了 R5 巨噬细胞趋向性的其他包膜决定因素。我们比较了一个人的大脑和淋巴结标本的高度巨噬细胞亲性 (B33) 和非巨噬细胞亲性 (LN40) 包膜。我们首先检查了残基 283 在巨噬细胞趋向性中的作用。将 N283 引入 LN40 (T283N) 赋予巨噬细胞高效的感染性。相比之下，用 N283 替换 B33 中更保守的苏氨酸对巨噬细胞感染几乎没有影响。因此，B33 携带独立于 N283 的巨噬细胞趋向性决定因素。我们制备了嵌合 B33/LN40 包膜，并使用定点诱变来鉴定其他决定因素。已鉴定的巨噬细胞向性的决定因素包括靠近 CD4 接触残基的 CD4 结合环侧翼上的残基和 V3 环中的残基。相同的残基影响对 CD4-免疫球蛋白 G 抑制的敏感性，与改变的 env-CD4 亲和力一致。我们预测这些决定因素会改变 CD4 接触残基的暴露。此外，CD4结合环侧翼是可变的，并且可能有助于保护近端CD4接触残基免受中和抗体影响的一般机制。我们的结果与基于 env 的疫苗相关，这些疫苗需要将关键的 CD4 接触残基暴露给免疫系统。
Human immunodeficiency virus type 1 R5 viruses vary extensively in phenotype. Thus, R5 envelopes (env) in the brain tissue of individuals with neurological complications are frequently highly macrophage-tropic. Macrophage tropism correlates with the capacity of the envelope to exploit low CD4 levels for infection. In addition, the presence of an asparagine at residue 283 within the CD4 binding site has been associated with brain-derived envelopes, increased env-CD4 affinity, and enhanced macrophage tropism. Here, we identify additional envelope determinants of R5 macrophage tropism. We compared highly macrophage-tropic (B33) and non-macrophage-tropic (LN40) envelopes from brain and lymph node specimens of one individual. We first examined the role of residue 283 in macrophage tropism. Introduction of N283 into LN40 (T283N) conferred efficient macrophage infectivity. In contrast, substitution of N283 for the more conserved threonine in B33 had little effect on macrophage infection. Thus, B33 carried determinants for macrophage tropism that were independent of N283. We prepared chimeric B33/LN40 envelopes and used site-directed mutagenesis to identify additional determinants. The determinants of macrophage tropism that were identified included residues on the CD4 binding loop flanks that were proximal to CD4 contact residues and residues in the V3 loop. The same residues affected sensitivity to CD4-immunoglobulin G inhibition, consistent with an altered env-CD4 affinity. We predict that these determinants alter exposure of CD4 contact residues. Moreover, the CD4 binding loop flanks are variable and may contribute to a general mechanism for protecting proximal CD4 contact residues from neutralizing antibodies. Our results have relevance for env-based vaccines that will need to expose critical CD4 contact residues to the immune system.