Department of Life and Environmental Sciences, Faculty of Engineering, Chiba Institute of Technology, Narashino-shi, Chiba 275-0016, Japan.
Nucleic Acids Res. 2010 Nov;38(21):7822-9. doi: 10.1093/nar/gkq615. Epub 2010 Jul 30.
Aptamers are short single-stranded nucleic acids with high affinity to target molecules and are applicable to therapeutics and diagnostics. Regardless of an increasing number of reported aptamers, the structural basis of the interaction of RNA aptamer with proteins is poorly understood. Here, we determined the 2.15 Å crystal structure of the Fc fragment of human IgG1 (hFc1) complexed with an anti-Fc RNA aptamer. The aptamer adopts a characteristic structure fit to hFc1 that is stabilized by a calcium ion, and the binding activity of the aptamer can be controlled many times by calcium chelation and addition. Importantly, the aptamer-hFc1 interaction involves mainly van der Waals contacts and hydrogen bonds rather than electrostatic forces, in contrast to other known aptamer-protein complexes. Moreover, the aptamer-hFc1 interaction involves human IgG-specific amino acids, rendering the aptamer specific to human IgGs, and not crossreactive to other species IgGs. Hence, the aptamer is a potent alternative for protein A affinity purification of Fc-fusion proteins and therapeutic antibodies. These results demonstrate, from a structural viewpoint, that conformational plasticity and selectivity of an RNA aptamer is achieved by multiple interactions other than electrostatic forces, which is applicable to many protein targets of low or no affinity to nucleic acids.
适体是具有与靶分子高亲和力的短单链核酸，适用于治疗和诊断。尽管越来越多的适体被报道，但 RNA 适体与蛋白质相互作用的结构基础仍了解甚少。在这里，我们确定了与人 IgG1（hFc1）Fc 片段复合物的抗 Fc RNA 适体的 2.15Å 晶体结构。该适体采用适合 hFc1 的特征结构，并通过钙离子稳定，并且通过钙螯合和添加可以多次控制适体的结合活性。重要的是，与其他已知的适体-蛋白质复合物相比，适体-hFc1 相互作用主要涉及范德华力和氢键，而不是静电力。此外，适体-hFc1 相互作用涉及人 IgG 特异性氨基酸，使适体特异性针对人 IgG，而不与其他物种 IgG 发生交叉反应。因此，该适体是 Fc 融合蛋白和治疗性抗体的蛋白 A 亲和纯化的有效替代品。这些结果从结构角度表明，RNA 适体的构象灵活性和选择性是通过除静电力以外的多种相互作用实现的，这适用于对核酸亲和力低或没有亲和力的许多蛋白质靶标。
