Impact of Lipid Composition and Receptor Conformation on the Spatio-temporal Organization of μ-Opioid Receptors in a Multi-component Plasma Membrane Model

Abstract

The lipid composition of cell membranes has increasingly been recognized as playing an important role in the function of various membrane proteins, including G Protein-Coupled Receptors (GPCRs). For instance, experimental and computational evidence has pointed to lipids influencing receptor oligomerization directly, by physically interacting with the receptor, and/or indirectly, by altering the bulk properties of the membrane. While the exact role of oligomerization in the function of class A GPCRs such as the μ-opioid receptor (MOR) is still unclear, insight as to how these receptors oligomerize and the relevance of the lipid environment to this phenomenon is crucial to our understanding of receptor function. To examine the effect of lipids and different MOR conformations on receptor oligomerization we carried out extensive coarse-grained molecular dynamics simulations of crystal structures of inactive and/or activated MOR embedded in an idealized mammalian plasma membrane composed of 63 lipid types asymmetrically distributed across the two leaflets. The results of these simulations point, for the first time, to specific direct and indirect effects of the lipids, as well as the receptor conformation, on the spatio-temporal organization of MOR in the plasma membrane. While sphingomyelin-rich, high-order lipid regions near certain transmembrane (TM) helices of MOR induce an effective long-range attractive force on individual protomers, both long-range lipid order and interface formation are found to be conformation dependent, with a larger number of different interfaces formed by inactive MOR compared to active MOR.

Separating Actin-Dependent Chemokine Receptor Nanoclustering from Dimerization Indicates a Role for Clustering in CXCR4 Signaling and Function

“…These nanoclusters are in dynamic equilibrium, with constant aggregation and dissociation to generate new receptor complexes (Calebiro et al, 2013). Many factors are involved in the regulation of GPCR nanoclustering (Calebiro et al, 2013;Hauser et al, 2016), including transmembrane proteins (Bethani et al, 2010), cell membrane lipid composition (Marino et al, 2016), and the actin cytoskeleton (Scarselli et al, 2012), which regulates trafficking of signaling molecules and partitions the membrane into microdomains (Kusumi et al, 2005). Nanoclustering and dynamics are especially relevant for chemokine receptors, as they allow the cell to correctly sense gradients and move appropriately.…”

State-dependent Lipid Interactions with the A2a Receptor Revealed by MD Simulations Using In Vivo-Mimetic Membranes

“…Recent CG simulations using bilayers composed of multiple lipid species have provided insights into GPCR-lipid interactions in a more biologically realistic environment (Ingolfsson et al, 2014;Koldso and Sansom, 2015). For example, the m-opioid receptor embedded in a complex lipid membrane was shown to induce lipid regions with high-order near certain transmembrane helices that may facilitate receptor dimerization (Marino et al, 2016). However, it remains unclear how GPCR-lipid interactions modulate the functions of GPCRs, such as receptor activation and downstream signaling, in a physiologically relevant context (i.e., in a lipid bilayer environment mimicking a mammalian cell membrane).…”

Insights into the function of opioid receptors from molecular dynamics simulations of available crystal structures

“…Capturing the oligomerization of GPCRs currently requires a coarse‐grained (CG) model, that is, a reduced representation with one bead describing multiple heavy atoms, since all‐atom MD simulations would be too computationally expensive. The MARTINI CG model has been used to study self‐assembly of a number of GPCRs, including opioid receptors (Provasi et al , ; Marino et al , ), rhodopsin (Periole et al , ; ), β 2 adrenoceptors (Prasanna et al , ) and the chemokine receptor CCR4 (Pluhackova et al , ). All‐atom MD has thus far only been applied to the preformed crystallographic dimers of the μ receptor and not their free association (Shim et al , ; Huang et al , ).…”

“…For instance, experiments have clearly shown that μ receptor oligomerization is sensitive to cholesterol levels (Zheng et al , ) and modulating serum cholesterol levels has been shown to affect the analgesic profile of opioids (Huang et al , ). To examine the effect of the lipids on opioid receptor oligomerization, we (Marino et al , ) recently examined the supramolecular organization of the inactive and/or activated conformations of the μ receptor in a 63‐component idealized plasma membrane model (Ingólfsson et al , ). These simulations suggested a specific mechanism by which lipid molecules appear to regulate the dimerization process of opioid receptors.…”