Structural Characterization of Natural Yeast Phosphatidylcholine and Bacterial Phosphatidylglycerol Lipid Multilayers by Neutron Diffraction

Abstract

Eukaryotic and prokaryotic cell membranes are difficult to characterize directly with biophysical methods. Membrane model systems, that include fewer molecular species, are therefore often used to reproduce their fundamental chemical and physical properties. In this context, natural lipid mixtures directly extracted from cells are a valuable resource to produce advanced models of biological membranes for biophysical investigations and for the development of drug testing platforms. In this study we focused on single phospholipid classes, i.e. Pichia pastoris phosphatidylcholine (PC) and Escherichia coli phosphatidylglycerol (PG) lipids. These lipids were characterized by a different distribution of their respective acyl chain lengths and number of unsaturations. We produced both hydrogenous and deuterated lipid mixtures. Neutron diffraction experiments at different relative humidities were performed to characterize multilayers from these lipids and investigate the impact of the acyl chain composition on the structural organization. The novelty of this work resides in the use of natural extracts with a single class head-group and a mixture of chain compositions coming from yeast or bacterial cells. The characterization of the PC and PG multilayers showed that, as a consequence of the heterogeneity of their acyl chain composition, different lamellar phases are formed.

Investigation on the relationship between lipid composition and structure in model membranes composed of extracted natural phospholipids

“…27 The combined experimental approach used in this work shed light on the interfacial structure of in vitro model systems of the plasma and ERGIC membranes, with emphasis on the structural effects associated with the incorporation of cholesterol in the membranes. Although natural lipids were previously used in the form of bi-and multilayers to mimic eukaryotic cell membranes, which were then characterized by neutron reflectometry 30,31 and diffraction 32,33 , to the best of our knowledge, this is the first report describing the use of natural lipids extracted from yeast and studied in the form of monolayers at the air/water interface, in order to mimic biological relevant membranes, and to provide direct structural evidences about the role of cholesterol. The possibility of tuning and controlling the composition and surface density of phospholipids makes Langmuir films effective models for mimicking single leaflets of cell membranes under different environmental conditions.…”

Lipid Bilayer Degradation Induced by SARS-CoV-2 Spike Protein as Revealed by Neutron Reflectometry

“…The natural phospholipid mixture contained phosphatidylcholine (PC), phosphatidylserine (PS) and phosphatidylethanolamine (PE) at the molar ratios PC:PS:PE:chol 59:20:11:10. The natural phospholipid mixtures were characterised by a polydisperse acyl chain length composition (C16-18) and a certain level of unsaturation (1-3 double bonds) 16,17 . Given the abundance of such lipid components and cholesterol in the mammalian plasma membrane 18 , they were chosen in our study to reproduce biologically relevant models of the plasma membrane 19 .…”

“…In this context, the use of deuterated lipids is particularly relevant for increasing the difference in scattering length density (neutron contrast) between lipids and proteins 22 . Therefore, to obtain the deuterated lipid mixtures, P. pastoris cells were grown in a deuterated culture medium 16,17,23,24 .…”