Lipid composition of Xenopus oocytes used for heterologous membrane protein expression.

Abstract

Biological membranes are characterized by a dynamic, heterogeneous lipid composition that can vary by cell type and species origin. Lipids are estimated to comprise 50% of the plasma membrane by weight. A growing body of evidence supports the view that membrane proteins and their adjacent lipids interact in a bidirectional manner. For example, lipid-protein interactions can affect protein function and contribute to membrane organization, such as the formation of domains. The Xenopus oocyte is a well-established classical heterologous expression system for the functional analysis of ion channels and transporters, especially those prevalent in neural tissue. This pilot research was undertaken with the goal of identifying lipids present in unfertilized Xenopus oocytes, specifically those known for their role in plasma membrane composition. Unfertilized Xenopus oocytes were purchased from a commercial vendor, frozen in liquid nitrogen, and shipped to the West Coast Metabolomics Center (WCMC) for lipid extraction. Six samples (20-30 oocytes each) were processed with an Agilent 6530B Q-TOF. During spectral analysis of the output LC/MS, over 1200 distinct lipids were identified. The MS-DIAL program (Version 4.48) assigned nomenclature and external database identifiers (InChI key; LIPIDMAPS) to 380 lipids that were grouped into 12 lipid subclasses, including canonical membrane lipids (phosphatidylcholine; phosphatidylethanolamine; sphingomyelin; ceramide; cholesterol). Estimates of relative abundance suggest that membrane lipids and triacylglycerols comprise 10% and 50% of the Xenopus oocyte lipidome, respectively. Preliminary findings may have implications for heterologous functional analysis of ion channels and other membrane transporters from the nervous system in Xenopus oocytes. Outcomes from this research are being incorporated into computational models of the membrane environment and lipid-protein interactions.