Dynamical Heterogeneity in Supported Lipid Bilayers
- PDF / 988,994 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 72 Downloads / 165 Views
Dynamical Heterogeneity in Supported Lipid Bilayers Liangfang Zhang and Steve Granick Abstract Planar-supported phospholipid bilayers are responsive surfaces that reconstruct when macromolecules adsorb. This review outlines the phenomenon of lipid diffusion “slaved” to or significantly controlled by that of macromolecular adsorbates. To elucidate such systems, we discuss the value of spatially resolved experiments at the few-molecule level, lipid diffusion compared in outer and inner leaflets of the supported bilayer, and a simple method to minimize defects by the strategy of “electrostatic stitching.” Keywords: adsorption, biological, diffusion, surface chemistry.
Consider the following armchair experiment. Suppose that you survey the audience in a movie theater. About half of the audience wears eyeglasses (two eyes per person, usually); about half of the audience wears none. On average, the number of eyes bearing eyeglasses is one per person. But this calculation is too simpleminded–– the naïve average masks a bimodal distribution that carries physical significance. So what? As this review will show, similar ideas apply to the case of phospholipids, where lipid mobilities have nontrivial distributions that depend strongly on macromolecular adsorbates. Lipid mobility in supported phospholipid bilayers is so fundamental to their function that it is interesting and relevant to understand the distribution of mobility within them, not just for studying biological questions but also in applied problems such as their use as biosensors and nanoreactors. Of central importance is understanding what controls the lateral mobility of the individual molecules that comprise these fluid yet two-dimensional systems.
“Slaved” Diffusion and the Value of Spatially Resolved Experiments A vast body of research shows that the presence of molecules such as cholesterol
MRS BULLETIN • VOLUME 31 • JULY 2006
embedded within the lipid membrane produces heterogeneities; for example, lipid “rafts” and resulting nanodomains are well documented.1–4 However, the simple process of allowing macromolecules to adsorb also produces dynamical heterogeneity, even when the bilayers are composed of one single type of phospholipid. It has been known for some time that lipid diffusion depends on the chemical composition and phase state of the bilayer,5–7 but those studies dealt with naked bilayers (no adsorption). It has also been known for some time that mixtures of phospholipids partition spatially after interacting with an adsorbate,8 but those studies did not address the mobility of these lipids. Other diffusion-related studies, such as binding-induced mobility,9–11 anomalous subdiffusion,12 and the influence of obstacles in the diffusing plane,13–15 have also been widely considered, but few of them involved macromolecule adsorption. The usual methods to study mobility in phospholipid bilayers employ areaaveraged methods, such as FRAP (fluorescence recovery after photobleaching), but an area-averaged method suffers from the same potential liability
Data Loading...
