Synthetic Analogues of Membrane Proteins

Abstract

Biological membranes carry a multitude of bound proteins and glycoproteins. These membrane-bound macromolecules confer on the membrane a variety of useful properties, including the capacity to respond to physical and chemical signals through changes in macromolecular conformation and solvation. We describe herein the preparation of synthetic or "semisynthetic" membranes that share with their natural counterparts two important characteristics: i). They are composed of a mixture of bilayer-forming lipids and bound macromolecules, and ii). They respond to well-defined chemical and physical signals via changes in macromolecular conformation and solvation. Poly(2-ethylacrylic acid) (PEAA) can be immobilized on phosphatidylcholine bilayer membranes by reaction of a thiolated derivative of the polymer with a membrane that includes a small amount of dimyristoyl N-[(4-maleimidomethyl)cyclohexanecarbonyl]phosphatidylethanolne. Bound and free polymer are readily separated by column chromatography. Typical preparations result in the irreversible binding of ca. 50 pg of PEAA per mg of lipid. Membranes prepared in this way are sensitive to hydrogen ion concentration, and are subject to large variations in permeability with small changes in pH. Rapid and quantitative release of vesicle contents can be achieved by mild acidification within the physiological pH range.

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