Direct observation of brownian motion of lipids in a membrane.
Nanovid microscopy, which uses 30- to 40-nm colloidal gold probes combined with video-enhanced contrast, can be used to examine random and directed movements of individual molecules in the plasma membrane of living cells. To validate the technique in a model system, the movements of lipid molecules were followed in a supported, planar bilayer containing fluorescein-conjugated phosphatidylethanolamine (Fl-PtdEtn) labeled with 30-nm gold anti-fluorescein (anti-Fl). Multivalent gold probes were prepared by conjugating only anti-Fl to the gold. Paucivalent probes were prepared by mixing an irrelevant antibody with the anti-Fl prior to conjugation. The membrane-bound gold particles moved in random patterns that were indistinguishable from those produced by computer simulations of two-dimensional random motion. The multivalent gold probes had an average lateral diffusion coefficient (D) of 0.26 x 10(-8) cm2/sec, and paucivalent probes had an average D of 0.73 x 10(-8) cm2/sec. Sixteen percent of the multivalent and 50% of the paucivalent probes had values for D in excess of 0.6 x 10(-8) cm2/sec, which, after allowance for stochastic variation, are consistent with the D of 1.3 x 10(-8) cm2/sec measured by fluorescence recovery after photobleaching of Fl-PtdEtn in the planar bilayer. The effect of valency on diffusion suggests that the multivalent gold binds several lipids forming a disk up to 30-40 nm in diameter, resulting in reduced diffusion with respect to the paucivalent gold, which binds one or a very few lipids. Provided the valency of the gold probe is considered in the interpretation of the results. Nanovid microscopy is a valid method for analyzing the movements of single or small groups of molecules within membranes.
Lee
G M
GM
Department of Cell Biology and Anatomy, University of North Carolina, Chapel Hill 27599-7090.
Ishihara
A
A
Jacobson
K A
KA
D000911:Antibodies, Monoclonal; D002784:Cholesterol / Q000737:chemistry*; D005456:Fluorescent Dyes; D006046:Gold; D017979:Gold Colloid; D008081:Liposomes; D008853:Microscopy / Q000379:methods; D008954:Models, Biological; D010712:Phosphatidic Acids / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry*; D013194:Staining and Labeling; D014741:Video Recording
D000911:Antibodies, Monoclonal; D005456:Fluorescent Dyes; D017979:Gold Colloid; D008081:Liposomes; D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; C063389:fluorescein phosphatidylethanolamine thiocarbamide; C058457:Aurodye; D006046:Gold; D002784:Cholesterol