Coupling Protonation States of Acid-Sensing Ion Channels to Dynamics and Function

Title: Coupling Protonation States of Acid-Sensing Ion Channels to Dynamics and Function
Authors: Miaro, Megan
Date: 2022-08-17
Abstract: Acid-sensing ion channels (ASICs) are trimeric, sodium-selective proton-gated ion channels. Having ligands as small as protons presents a challenge when studying the structure-function relationships of pH-dependent gating. Knowing where protons must bind to evoke a pH-dependent conformational change related to gating would provide one with insights into the molecular mechanisms underlying pH-dependent function in ASICs. We use molecular dynamics (MD) simulations that allow us to model explicit protons and directly examine the effects of changing protonation states on ASIC1 dynamics. We first combine the use of unbiased MD simulations with pKₐ prediction on the three functional states of cASIC1 to identify the effects of protonation state changes on interactions between ionizable residues in the acidic pocket (ACP), a region rich in acidic residues in the protein that plays a role in pH-sensing. We interpret the importance of E98, a buried residue in the ACP with a highly shifted pKₐ value, as well as the positively charged R191, also in the ACP, which has a flexible side chain and can interact with multiple negatively charged side chains, and the role of these residues in the pH-dependent collapse of the ACP. Additionally, we identify a hydrogen-bond network in the palm domain that consists of the Q277 side chain that interacts with the E80 side chain and L414 backbone carbonyl. This network contributes to a stable desensitized state and is stabilized by an E80-/E412H/E417H protonation configuration. Next, targeted MD was combined with pKₐ prediction to simulate the full transition pathways and to link protonation states with the molecular mechanisms involved in conformational changes. Our results suggest four residues, E98, E314, H328, and E374, that may be important in pH-sensing and gating, and that require further functional investigation in the context of activation and desensitization. This research exemplifies how MD is a useful tool in studying how protonation directly affects the structural dynamics of a protein and how it can complement existing functional studies and be used to suggest future experimental investigations.
CollectionThèses, 2011 - // Theses, 2011 -