Structural biology of human GPCR drugs and endogenous ligands - insights from NMR spectroscopy

Global insights into the fine tuning of human A2AAR conformational dynamics in a ternary complex with an engineered G protein viewed by NMR

G protein-coupled receptor (GPCR) conformational plasticity enables formation of ternary signaling complexes with intracellular proteins in response to binding extracellular ligands. We investigate the dynamic process of GPCR complex formation in solution with the human A_2A adenosine receptor (A_2AAR) and an engineered G_s protein, mini-G_s. 2D nuclear magnetic resonance (NMR) data with uniform stable isotope-labeled A_2AAR enabled a global comparison of A_2AAR conformations between complexes with an agonist and mini-G_s and with an agonist alone. The two conformations are similar and show subtle differences at the receptor intracellular surface, supporting a model whereby agonist binding alone is sufficient to populate a conformation resembling the active state. However, an A_2AAR "hot spot" connecting the extracellular ligand-binding pocket to the intracellular surface is observed to be highly dynamic in the ternary complex, suggesting a mechanism for allosteric connection between the bound G protein and the drug-binding pocket involving structural plasticity of the "toggle switch" tryptophan.

Conformational dynamics in peptide toxins: Implications for receptor interactions and molecular design

Peptide toxins are potent and often exquisitely selective probes of the structure and function of ion channels and receptors, and are therefore of significant interest to the pharmaceutical and biotech industries as both pharmacological tools and therapeutic leads. The three-dimensional structures of peptide toxins are essential as a basis for understanding their structure-activity relationships and their binding to target receptors, as well as in guiding the design of analogues with modified potency and/or selectivity for key targets. NMR spectroscopy has played a key role in elucidating the structures of peptide toxins and probing their structure-function relationships. In this article, we highlight the additional important contribution of NMR to characterising the dynamics of peptide toxins. We also compare the information available from NMR measurements with that afforded by molecular dynamics simulations. We describe several examples of the importance of dynamics measurements over a range of timescales for understanding the structure-function relationships of peptide toxins and their receptor engagement. Peptide toxins that inhibit the voltage-gated potassium channel K_V1.3 with pM affinities display different degrees of conformational flexibility, even though they contain multiple disulfide bonds, and this flexibility can affect the relative orientation of residues that have been shown to be critical for channel binding. Information on the dynamic properties of peptide toxins is important in the design of analogues or mimetics where receptor-bound structures are not available.

Function-Related Dynamics in Multi-Spanning Helical Membrane Proteins Revealed by Solution NMR

A primary biological function of multi-spanning membrane proteins is to transfer information and/or materials through a membrane by changing their conformations. Therefore, particular dynamics of the membrane proteins are tightly associated with their function. The semi-atomic resolution dynamics information revealed by NMR is able to discriminate function-related dynamics from random fluctuations. This review will discuss several studies in which quantitative dynamics information by solution NMR has contributed to revealing the structural basis of the function of multi-spanning membrane proteins, such as ion channels, GPCRs, and transporters.