Coarse-Grained Simulations Suggest the Epsin N-Terminal Homology Domain Can Sense Membrane Curvature without Its Terminal Amphipathic Helix.

Alexis Belessiotis-Richards,Mark S P Sansom,Alfredo Alexander-Katz,Molly M Stevens,Stuart G Higgins

doi:10.1021/acsnano.0c05960

Alexis Belessiotis-Richards, Mark S P Sansom + Show 3 more

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https://doi.org/10.1021/acsnano.0c05960

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Abstract

Nanoscale membrane curvature is a common feature in cell biology required for functions such as endocytosis, exocytosis and cell migration. These processes require the cytoskeleton to exert forces on the membrane to deform it. Cytosolic proteins contain specific motifs which bind to the membrane, connecting it to the internal cytoskeletal machinery. These motifs often bind charged phosphatidylinositol phosphate lipids present in the cell membrane which play significant roles in signaling. These lipids are important for membrane deforming processes, such as endocytosis, but much remains unknown about their role in the sensing of membrane nanocurvature by protein domains. Using coarse-grained molecular dynamics simulations, we investigated the interaction of a model curvature active protein domain, the epsin N-terminal homology domain (ENTH), with curved lipid membranes. The combination of anionic lipids (phosphatidylinositol 4,5-bisphosphate and phosphatidylserine) within the membrane, protein backbone flexibility, and structural changes within the domain were found to affect the domain’s ability to sense, bind, and localize with nanoscale precision at curved membrane regions. The findings suggest that the ENTH domain can sense membrane curvature without the presence of its terminal amphipathic α helix via another structural region we have denoted as H3, re-emphasizing the critical relationship between nanoscale membrane curvature and protein function.

Highlights

Nanoscale membrane curvature is a common feature in cell biology required for functions such as endocytosis, exocytosis and cell migration
The epsin Nterminal homology domain (ENTH) domain has been shown to spontaneously localize and sense membrane curvature both experimentally and in theoretical studies, and it has become a model for curvature active protein domains.[16−19] A number of reports have suggested that hydrophobic insertion of amphipathic helices is a key mechanism for membrane curvature generation in cells.[20−22] Many curvatureactive proteins contain amphipathic helices such as N-BARcontaining proteins involved in endocytosis, as well as Arf[1] and Sarlp.[23,24]
We have previously assumed PIP2 to be a necessary, yet neutral player in the complex act of membrane curvature sensing, but could it be that PIP2 lipids play a more active role in this process? In this work, we study a model curvature sensing protein, the ENTH domain, and its interaction with curvature and with its key binding partner, PIP2

Summary

Introduction

Nanoscale membrane curvature is a common feature in cell biology required for functions such as endocytosis, exocytosis and cell migration. Especially the presence of anionic lipids, plays a significant role in modulating curvature activity of amphipathic helixcontaining proteins.[25−27] Chen et al suggests hydrophobic residue insertion may only play a minor role in membrane curvature generation.[28] Zeno et al showed that membrane curvature sensing occurs in disordered proteins via purely nonspecific interactions, suggesting that electrostatic and entropic forces can drive curvature sensing without the presence of a structural sensing motif.[29] recent work by Mu et al has shown that PIP2 localization to regions of membrane curvature is key to initiating an ancient Moesinbased phagocytotic pathway which is suggested to have been at the origin of receptor-mediated phagocytosis.[30] hydrophobic insertion is an accepted mechanism for membrane curvature sensing, it has not been explored at the molecular level in combination with PIP2. For each of these permutations, we studied the interaction of the domains with curved phosphatidylcholine (PC) membranes containing various proportions of negatively charged lipids. The three membrane variants investigated were: pure PC, PC with 12.5% phosphatidylserine (PS), and PC with 2.5% PIP2

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