Abstract：
Valinomycin (VM) is a natural K+-selective ionophore that transports K+ through the cell membrane. VM captures K+ in its central cavity with a C3-symmetric β-turn-like backbone. Although the binding affinity is drastically decreased for the VM-sodium (Na+VM) complex with respect to K+VM, VM holds relatively high affinity to Rb+ and Cs+. The high affinity for larger ions irrespective of ionic size seems to conflict with the expected optimal size matching model and raises questions on what factors determine ion selectivity. A combination of infrared spectroscopy with supporting computational calculations reveals that VM can accommodate larger Rb+ and Cs+ by flexibly changing its cavity size with the elongation of its folded β-turn-like backbone. The high affinity to Rb+ and Cs+ can be ascribed to a size-dependent cavity expansion. These findings provide a new perspective on molecular recognition and selectivity beyond the conventional size matching model.
摘要：
Valinomycin（VM）是一种天然的K选择性离子载体，可通过细胞膜转运K。VM在其中央腔中捕获K，并带有C3对称的β转角状骨架。尽管VM-钠（NaVM）复合物相对于KVM的结合亲和力急剧下降，VM对Rb+和Cs+具有相对高的亲和力。无论离子大小如何，对较大离子的高亲和力似乎与预期的最佳大小匹配模型相冲突，并引发了关于哪些因素决定离子选择性的问题。红外光谱与支持计算的结合表明，VM可以通过灵活地改变其折叠的β弯状骨架的伸长来容纳更大的Rb和Cs。对Rb+和Cs+的高亲和力可归因于尺寸依赖性腔扩张。这些发现提供了超越常规尺寸匹配模型的分子识别和选择性的新观点。
