{Reference Type}: Journal Article
{Title}: Cation-responsive cavity expansion of valinomycin revealed by cryogenic ion trap infrared spectroscopy.
{Author}: Hirata K;Sato E;Lisy JM;Ishiuchi SI;Fujii M;
{Journal}: Phys Chem Chem Phys
{Volume}: 25
{Issue}: 2
{Year}: Jan 2023 4
{Factor}: 3.945
{DOI}: 10.1039/d2cp04570b
{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.