Abstract
The plasma membrane is an important organelle providing structure, signaling and transport as major biological functions. Being composed of lipids and proteins with different physicochemical properties, the biological functions of membranes depend on specific protein–protein and protein–lipid interactions. Interactions of proteins with their specific sterol and lipid environment were shown to be important factors for protein recruitment into sub-compartmental structures of the plasma membrane. System-wide implications of altered endogenous sterol levels for membrane functions in living cells were not studied in higher plant cells. In particular, little is known how alterations in membrane sterol composition affect protein and lipid organization and interaction within membranes. Here, we conducted a comparative analysis of the plasma membrane protein and lipid composition in Arabidopsis sterol-biosynthesis mutants smt1 and ugt80A2;B1. smt1 shows general alterations in sterol composition while ugt80A2;B1 is significantly impaired in sterol glycosylation. By systematically analyzing different cellular fractions and combining proteomic with lipidomic data we were able to reveal contrasting alterations in lipid–protein interactions in both mutants, with resulting differential changes in plasma membrane signaling status.
Highlights
The plasma membrane contains numerous lipid species with different physicochemical properties
DETECTION OF STEROL-DEPENDENT PROTEIN CANDIDATES BY detergent-resistant membrane (DRM)/detergent soluble fraction (DSF) DISTRIBUTION ANALYSIS To characterize the role of sterol composition for the localization of proteins within membrane microdomains, we studied the distribution of proteins between sterol-rich and sterol depleted membrane fractions
By comparing abundances of proteins identified in DRM and DSF against abundances in fractions of soluble proteins (SP) and intracellular membranes (IM), co-purifying proteins were defined if their highest abundance was either in SP or IM
Summary
The plasma membrane contains numerous lipid species with different physicochemical properties. Spontaneous phase separation was shown to occur in artificial membranes involving mainly lipids of higher hydrophobicity such as sphingolipids, sterols or long-chain phospholipids (Karnovsky et al, 1982; Thompson and Tillack, 1985). These experiments extended the fluid mosaic model of Singer and Nicolson (Singer and Nicolson, 1972) of protein–lipid organization by adding subcompartmental occurrences of specific protein and lipid compositions in the plasma membrane in so-called microdomains. Support for this model in plants came from stimulus-dependent membrane microdomain localization of the Arabidopsis flagellin receptor and the ion channel SLAH3 using a combination of proteomic and cell biology approaches (Keinath et al, 2010; Demir et al, 2013)
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