Martín Verónica, Domingo Esteban
Centro de Biología Molecular "Severo Ochoa" (CSIC-UAM), C/Nicolás Cabrera, Universidad Autónoma de Madrid, Cantoblanco, Madrid, Spain.
Mol Biol Evol. 2008 Aug;25(8):1544-54. doi: 10.1093/molbev/msn099. Epub 2008 Apr 23.
RNA viruses replicate as complex mutant distributions termed viral quasispecies. Despite this, studies on virus populations subjected to positive selection have generally been performed and analyzed as if the viral population consisted of a defined genomic nucleotide sequence; such a simplification may not reflect accurately the molecular events underlying the selection process. In the present study, we have reconstructed a foot-and-mouth disease virus quasispecies with multiple, low-frequency, genetically distinguishable mutants that can escape neutralization by a monoclonal antibody. Some of the mutants included an amino acid substitution that affected an integrin recognition motif that overlaps with the antibody-binding site, whereas other mutants included an amino acid substitution that affected antibody binding but not integrin recognition. We have monitored consensus and clonal nucleotide sequences of populations passaged either in the absence or the presence of the neutralizing antibody. In both cases, the populations focused toward a specific mutant that was surrounded by a cloud of mutants with different antigenic and cell recognition specificities. In the absence of antibody selection, an antigenic variant that maintained integrin recognition became dominant, but the mutant cloud included as one of its minority components a variant with altered integrin recognition. Conversely, in the presence of antibody selection, a variant with altered integrin recognition motif became dominant, but it was surrounded by a cloud of antigenic variants that maintained integrin recognition. The results have documented that a mutant spectrum can exert an influence on a viral population subjected to a sustained positive selection pressure and have unveiled a mechanism of antigenic flexibility in viral populations, consisting in the presence in the selected quasispecies of mutants with different antigenic and cell recognition specificities.
RNA病毒以称为病毒准种的复杂突变分布形式进行复制。尽管如此，对受到正选择的病毒群体的研究通常是按照病毒群体由确定的基因组核苷酸序列组成来进行和分析的；这种简化可能无法准确反映选择过程背后的分子事件。在本研究中，我们重建了一种口蹄疫病毒准种，它具有多个低频、基因上可区分的突变体，这些突变体能够逃避单克隆抗体的中和作用。一些突变体包含一个影响与抗体结合位点重叠的整合素识别基序的氨基酸替换，而其他突变体包含一个影响抗体结合但不影响整合素识别的氨基酸替换。我们监测了在不存在或存在中和抗体的情况下传代群体的共有和克隆核苷酸序列。在这两种情况下，群体都趋向于一个特定的突变体，该突变体被具有不同抗原和细胞识别特异性的突变体云所包围。在没有抗体选择的情况下，保持整合素识别的抗原变体占主导地位，但突变体云包含一个整合素识别改变的变体作为其少数成分之一。相反，在有抗体选择的情况下，整合素识别基序改变的变体占主导地位，但它被保持整合素识别的抗原变体云所包围。结果证明了突变谱可以对受到持续正选择压力的病毒群体产生影响，并揭示了病毒群体中抗原灵活性的机制，即在选定的准种中存在具有不同抗原和细胞识别特异性的突变体。
