Non-detergent Isolation of Membrane Structures from Beet Plasmalemma and Tonoplast Having Lipid Composition Characterist
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Non‑detergent Isolation of Membrane Structures from Beet Plasmalemma and Tonoplast Having Lipid Composition Characteristic of Rafts Natalia V. Ozolina1 · Irina S. Nesterkina1 · Veronika V. Gurina1 · Vadim N. Nurminsky1 Received: 29 April 2020 / Accepted: 26 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Vacuolar and plasma membranes were isolated by a detergent-free method from beet roots (Beta vulgaris L.), and were fractionated in a sucrose density gradient of 15–60% by high-speed centrifugation at 200,000×g during 18 h. The membrane material distributed over the sucrose density gradient was analyzed for the presence of lipids characteristic of raft structures in different zones of the gradient. The quantitative and qualitative content of lipids and sterols, and the composition of fatty acids were analyzed. Some membrane structures differing in their biochemical characteristics were revealed to be located in different zones of the sucrose gradient. The results of the analysis allowed us to identify three zones in the sucrose gradient after the vacuolar membrane fractionation and two zones in the plasma membrane where membrane structures, which may be defined as rafts for their lipid composition, were presented. Graphic Abstract
Keywords Membrane lipids · Tonoplast · Plasma membrane · Rafts
Introduction * Vadim N. Nurminsky [email protected] 1
Siberian Institute of Plant Physiology and Biochemistry, Siberian Branch, Russian Academy of Sciences, 132, Lermontov st., Irkutsk 664033, Russia
The intensive study of the structure of biological membranes has led to the understanding that cell membranes are very heterogeneous. It is now generally accepted that lipid–protein microdomains (rafts) are present in membranes (Simons and Ikonen 1997; Pike 2004; Lingwood and Simons 2010). Rafts are characterized as microdomains of the lipid bilayer
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of cell membranes, in which regions with denser packing of lipid molecules are formed around certain proteins. These regions are enriched with glycosphingolipids, sterols, and lipids with saturated fatty acids (Brown and London 2000; Sengupta et al. 2007). Rafts isolated from the different membranes may differ both in their biochemical composition and in their functions (Harder and Simons 1999). The protein component of rafts is represented by aquaporins, ATPases, caveolins, G-proteins, protein kinases, and it may differ substantially (Sengupta et al. 2007). The lipid component is more conservative than the protein one. According to the definition of lipid rafts, their lipid component should be dominated by certain groups of lipids, primarily sterols, sphingolipids, and ceramides. However, lipid composition and ratio may also vary. Changing lipid component of rafts influences some biophysical parameters, such as fluidity, rigidity, and flexibility. In addition to biophysical aspect, differences in lipid composition of rafts also relate to their functions since the lipids these rafts consist of can take on t
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