Isolation of AtSWEET Membrane Proteins from Arabidopsis Leaves for Host-Pathogen Interaction Studies

Optimizing the conditions for the overexpression and purification of membrane proteins for functional and structural studies is a complex and tedious process, which demands considerable time and effort. Membranes are made up of phospholipid bilayer embedded with proteins, cholesterol, and carbohydrates. While cholesterol regulates the fluidity, proteins and carbohydrates provide functionality to the membranes. Membrane proteins are responsible for transport, signaling, adhesion, and catalysis and have membrane spanning domains that tether them to the lipid bilayer. Due to the hydrophobic nature of these membrane spanning domains, isolation, and biochemical analysis becomes challenging. For an extended period, researchers have refined techniques to achieve the highest purity in plasma membrane vesicle preparations derived from crude plant extracts. While, conventional detergent-based isolation methods can solubilize both globular and membrane proteins, an enrichment step is necessary to remove cytosolic or aggregated contaminants. The current protocol outlines a method for membrane purification utilizing ultracentrifugation and detergents, which facilitates the isolation of membrane proteins in their native conformational state.