激发态在蛋白质的折叠、酶催化和分子识别等生物学功能上发挥关键作用。由于激发态的丰度太低，大多数的结构生物学方法难以表征激发态的构象。针对基态-激发态交换时间尺度在约2-100毫秒的慢交换体系，化学交换饱和传递（CEST）可直观测量激发态的化学位移。然而仅通过化学位移来重构激发态构象面临着巨大的挑战。我们近期开发了激发态赝接触位移测量的新方法，可获得激发态的距离和取向相关的关键结构信息。在此基础上，拟以胆酸结合蛋白FABP6等具有构象选择特性的1-2个慢交换体系为研究对象，发展完善赝接触位移及残余偶极耦合与CEST联用的新技术，依托稳态强磁场中心的高分辨率850 MHz核磁共振谱仪，获得低丰度激发态的化学位移、多套赝接触位移和残余偶极耦合数据，在这些重要结构约束的基础上尝试首次搭建慢交换体系的激发态结构模型。这将阐明预先存在的激发态构象在蛋白-配基分子识别的构象选择机制上所发挥的关键作用。

Despite the critical roles of excited states in protein folding, catalysis and molecular recognition, they remain intractable for most structural studies because of their notably low populations. Chemical shifts for "invisible" states in slow exchanging with the ground state (~2-100 ms) are intuitively observed using NMR chemical exchange saturation transfer (CEST) experiments. It, however, remains a great challenge to rebuild the excited-state conformations using chemical shifts only. We have recently developed a new method to determine pseudocontact shifts of excited states, which carry valuable angular and distance information in these states. We, therefore, plan to study one or two slow exchanging systems with a characteristic conformational selection mechanism for protein-ligand recognition, e.g., the bile acid binding protein FABP6. We will further develop CEST based approaches to determine pseudocontact shifts and residual dipolar couplings of excited states, using the high resolution 850 MHz spectrometer in the High Magnetic Field Laboratory, CAS. Based on the critical structural restraints of chemical shifts, multiple pseudocontact shift datasets, and multiple independent residual dipolar coupling datasets for the low-populated excited states, we plan to generate for the first time the structural model of the excited states in a slow exchanging system. It enables the elucidation of the essential role of the pre-existing excited states in the conformational selection mechanism for protein-ligand recognition.