W246^6.48 Opens a Gate for a Continuous Intrinsic Water Pathway during Activation of the Adenosine A_2A Receptor

Abstract

The question how G-protein-coupled receptors transduce an extracellular signal by a sequence of transmembrane conformational transitions into an intracellular response remains to be solved at molecular detail. Herein, we use molecular dynamics simulations to reveal distinct conformational transitions of the adenosine A2A receptor, and we found that the conserved W246(6.48) residue in transmembrane helix TM6 performs a key rotamer toggle switch. Agonist binding induces the sidechain of W246(6.48) to fluctuate between two distinct conformations enabling the diffusion of water molecules from the bulk into the center of the receptor. After passing the W246(6.48) gate, the internal water molecules induce another conserved residue, Y288(7.53), to switch to a distinct rotamer conformation establishing a continuous transmembrane water pathway. Further, structural changes of TM6 and TM7 induce local structural changes of the adjacent lipid bilayer.

Enhancing Structure Prediction and Design of Soluble and Membrane Proteins with Explicit Solvent-Protein Interactions

“…G protein-coupled receptors (GPCRs)) are believed to exchange directly with the polar phases of the protein environment (i.e. lipid headgroup and water phase) similarly to soluble proteins (Figure 1) (Yuan et al, 2014; Yuan et al, 2015). Therefore, the aqueous phase is an appropriate reference state for the solvent molecules in membrane proteins.…”

“…Tyr 7.53) from the conserved NPxxY motif. Receptor activation upon ligand agonist and G protein binding involves a major rearrangement of solvent-mediated interactions in the receptor TMH region, remodeling the solvated cavities and solvent penetration in the receptor (Yuan et al, 2014; Yuan et al, 2015). These observations strongly suggest that solvent molecules participate to the allosteric pathways transmitting structural and dynamic changes from the extracellular to the intracellular sides of the receptor structure.…”

Structural heterogeneity of the μ-opioid receptor’s conformational ensemble in the apo state

“…The latter, along with the intracellular halves of TMs 2, 3, and 6 rearrange so as to open a ‘hydrophobic barrier’4. This concerts with the so-called ‘rotamer toggle switch’ to form a water channel connecting the extra- and intracellular sides891011. Between the toggle switch and the hydrophobic barrier lies the allosteric sodium binding pocket (Fig.…”

Mechanistic Studies on the Stereoselectivity of the Serotonin 5‐HT1A Receptor

“…Subtle fluctuations also were observed for W358 6.48 in the complex with the antagonist at the beginning of the simulations, but these returned to the starting conformation after 700 ns (Figure 2B). Our previous studies of the adenosine and opioid receptors [6,21] revealed W358 6.48 to be a central molecular switch that enables the formation of an internal continuous water channel within the receptor, which was proposed to be a hallmark of GPCR activation. In the present case of the 5-HT 1A receptor, we again observed the side-chain rotational switch associated with W358 6.48 , and therefore we also analyzed water movement inside the 5-HT 1A receptor.…”

“…The existence of such hydrophobic layers of amino acids agrees with the disruption of water-mediated hydrogen-bond networks observed in GPCR crystal structures [22,23] and in MD simulations. [6, 7, 21, 24] …”