CAS Key Laboratory for Biomedical Effects of Nanomaterials & Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences (CAS), Beijing 100049, China.
Nanoscale. 2014 Nov 7;6(21):12828-37. doi: 10.1039/c4nr01623h.
There are growing concerns about the biosafety of nanomaterials such as carbon nanotubes (CNTs) as their applications become more widespread. We report here a theoretical and experimental study of the binding of various sizes of CNTs [CNT (4,4), (5,5), (6,6) and (7,7)] to calmodulin (CaM) protein and, in particular, their impact on the Ca(2+)-dependent dynamic properties of CaM. Our simulations show that all the CNTs can plug into the hydrophobic binding pocket of Ca(2+)-bound CaM with binding affinities comparable with the native substrate M13 peptide. Even though CNT (4,4) shows a similar behavior to the M13 peptide in its dissociation from Ca(2+)-free CaM, wider CNTs still bind firmly to CaM, indicating a potential failure of Ca(2+) regulation. Such a size-dependent impact of CNTs on the dynamic properties of CaM is a result of the excessively strong hydrophobic interactions between the wider CNTs and CaM. These simulation results were confirmed by circular dichroism spectroscopy, which showed that the secondary structures of CaM become insensitive to Ca(2+) concentrations after the addition of CNTs. Our findings indicate that the cytotoxicity of nanoparticles to proteins arises not only from the inhibition of static protein structures (binding pockets), but also from impacts on their dynamic properties.
人们越来越关注碳纳米管（CNTs）等纳米材料的生物安全性，因为它们的应用越来越广泛。我们在此报告了一项关于不同大小的 CNTs[CNT（4,4）、（5,5）、（6,6）和（7,7）]与钙调蛋白（CaM）结合的理论和实验研究，特别是它们对 CaM 依赖 Ca2+的动态特性的影响。我们的模拟表明，所有的 CNTs 都可以插入到 Ca2+-结合的 CaM 的疏水性结合口袋中，与天然底物 M13 肽的结合亲和力相当。尽管 CNT（4,4）在与 Ca2+-游离 CaM 的解离中表现出与 M13 肽相似的行为，但更宽的 CNTs 仍然与 CaM 牢固结合，这表明 Ca2+调节可能失效。这种 CNT 对 CaM 动态特性的尺寸依赖性是由于更宽的 CNT 与 CaM 之间的过度强疏水性相互作用造成的。这些模拟结果得到了圆二色性光谱的证实，该光谱表明在加入 CNTs 后，CaM 的二级结构对 Ca2+浓度变得不敏感。我们的发现表明，纳米颗粒对蛋白质的细胞毒性不仅源于对静态蛋白质结构（结合口袋）的抑制，还源于对其动态特性的影响。
