Abstract
Characterization of the two-dimensional organization of biological membranes is one of the most important issues that remains to be achieved in order to understand their structure-function relationships. According to the current view, biological membranes would be organized in in-plane functional microdomains. At least for one category of them, called rafts, the lateral segregation would be driven by lipid-lipid interactions. Basic questions like the size, the kinetics of formation, or the transbilayer organization of lipid microdomains are still a matter of debate, even in model membranes. Because of its capacity to image structures with a resolution that extends from the molecular to the microscopic level, atomic force microscopy (AFM) is a useful tool for probing the mesoscopic lateral organization of lipid mixtures. This paper reviews AFM studies on lateral lipid domains induced by lipid-lipid interactions in model membranes.
Highlights
Whereas the asymmetrical distribution of phospholipids and glycolipids between the exoplasmic and cytoplasmic leaflets of plasma membranes was clearly established in the 1970s[1], the inplane organization of membrane constituents remains poorly understood
Bilayers made from 1:3 SM/POPC mixtures, which would correspond to a total SM content of ~10–15 mol% in the plasma membrane, i.e., a value commonly found in many cell types, show the presence of small liquid condensed (LC) microdomains dispersed in the liquid expanded (LE) matrix (Fig. 5A)
Most studies were performed on two-component, gel-fluid phases lipid bilayers, the model privileged by biophysicists interested in characterizing membrane lateral heterogeneity
Summary
Pierre Emmanuel Milhiet, Marie-Cécile Giocondi, and Christian Le Grimellec*,1. Received April 20, 2002; Revised June 19, 2002; Accepted June 24, 2002; Published March 17, 2003. Characterization of the two-dimensional organization of biological membranes is one of the most important issues that remains to be achieved in order to understand their structure-function relationships. According to the current view, biological membranes would be organized in in-plane functional microdomains. Basic questions like the size, the kinetics of formation, or the transbilayer organization of lipid microdomains are still a matter of debate, even in model membranes. Because of its capacity to image structures with a resolution that extends from the molecular to the microscopic level, atomic force microscopy (AFM) is a useful tool for probing the mesoscopic lateral organization of lipid mixtures. This paper reviews AFM studies on lateral lipid domains induced by lipid-lipid interactions in model membranes. DOMAINS: biophysics, biochemistry, physical and theoretical chemistry, structural biology, cell biology, microscopy
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