Force Field Comparison of GM1 in a DOPC Bilayer Validated with AFM and FRET Experiments Michael C. Owen,* ,†,∥ Andreas Karner, ‡ Radek S ̌ achl, § Johannes Preiner, ‡ Mariana Amaro, § and Robert Va ́ cha †,∥ † CEITEC − Central European Institute of Technology, Kamenice 5, 625 00 Brno, Czech Republic ‡ University of Applied Sciences Upper Austria, 4020 Linz, Austria § Department of Biophysical Chemistry, J. Heyrovský Institute of Physical Chemistry of the C.A.S., v.v.i., Dolejs ̌ kova 2155/3, 182 23 Prague 8, Czech Republic ∥ Faculty of Science, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic * S Supporting Information ABSTRACT: The great physiological relevance of glycolipids is being increasingly recognized, and glycolipid interactions have been shown to be central to cell−cell recognition, neuronal plasticity, protein−ligand recognition, and other important processes. However, detailed molecular-level understanding of these processes remains to be fully resolved. Molecular dynamics simulations could reveal the details of the glycolipid interactions, but the results may be influenced by the choice of the employed force field. Here, we have compared the behavior and properties of GM1, a common, biologically important glycolipid, using the CHARMM36, OPLS, GROMOS, and Amber99-GLYCAM06 (in bilayers comprising SLIPIDS and LIPID14 lipids) force fields in bilayers comprising 1,2-dioleoyl-sn- glycero-3-phosphocholine lipids and compared the results to atomic force microscopy and fluorescence resonance energy transfer experiments. We found discrepancies within the GM1 behavior displayed between the investigated force fields. Based on a direct comparison with complementary experimental results derived from fluorescence and AFM measurements, we recommend using the Amber99-GLYCAM force field in bilayers comprising LIPID14 or SLIPIDS lipids followed by CHARMM36 and OPLS force fields in simulations. The GROMOS force field is not recommended for reproducing the properties of the GM1 head group. 1. INTRODUCTION Glycolipids are compounds that comprise one or more monosaccharides covalently bound to a lipid. The hydrophobic moiety of glycosphingolipids is a sphingolipid, typically a ceramide and in rare cases a sphingoid base (lysoglycosphin- golipids). 1 Glycosphingolipids can be amphoteric, basic, or acidic. Acidic glycosphingolipids that contain one or more sialic acid saccharides are known as gangliosides. 2 Gangliosides without a sialic acid moiety are known as asialo, whereas gangliosides with one, two, or three sialic acid groups are named mono-, di-, or tri-sialo, respectively, according to the Svennerholm nomenclature, which is the most often encountered in the literature. 3 The most abundant ganglioside in vertebrates is monosialoganglioside 1 (GM1), an a-series ganglioside found in neuronal white matter. After 1995, there was an increase in the quantification of gangliosides in lipids, and it has since been shown that GM1 is present in white matter tissue at a concentration of 2−4 mol % of the total membrane lipids, which can vary with age. 4−8 The structure of GM1 can be found in Scheme 1. GM1 participates in several cellular functions such as signal transduction, 9 cell−cell recognition, 10 neuronal differentiation, 11 and the formation of synapses 12 while embedded in membranes. These functions are mediated by the ability of GM1 and possibly other gangliosides to gather into cholesterol- and sphingolipid-rich raft domains. The factors that affect the formation and the stability of the domains are currently under rigorous investigation although it has been proposed that cholesterol is a key raft-stabilizing component. 13−15 Glycophospholipids are primarily synthesized in the endoplasmic reticulum and further modified by the Golgi apparatus by the subsequent addition of saccharides by glycosyltransferases. 16 Glycosyl- transferase dysregulation has been shown to cause several diseases, 2 including influenza, 17 lysosomal storage diseases such as GM1 (Tay−Sachs) and GM2 gangliosidosis (Sandh- off), and a form of epilepsy. 18 Moreover, the interaction between gangliosides and extracellular peptides is thought to mediate the pathology of neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. 19,20 To better elucidate the physiological role of gangliosides and to gain insight into mechanisms of the aforementioned diseases, the structure of the carbohydrate region of ganglio- sides needs to be characterized. Determining the extracellular orientation of the glycan region of complex gangliosides such as GM1 is further complicated by flexibility of the carbohydrate domain. The glycan region can exist in multiple, Received: May 29, 2019 Revised: August 2, 2019 Published: August 9, 2019 Article pubs.acs.org/JPCB Cite This: J. Phys. Chem. B 2019, 123, 7504-7517 © 2019 American Chemical Society 7504 DOI: 10.1021/acs.jpcb.9b05095 J. Phys. Chem. B 2019, 123, 7504−7517 Downloaded via ACADEMY OF SCIENCES CZECH REPUBLIC on October 4, 2019 at 16:31:54 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.