DETECTION OF TEMPORARY LATERAL CONFINEMENT OF MEMBRANE-PROTEINS USINGSINGLE-PARTICLE TRACKING ANALYSIS

Techniques such as single-particle tracking allow the characterization of the movements of single or very few molecules. Features of the mol ecular trajectories, such as confined diffusion or directed transport, can reveal interesting biological interactions, but they can also ari se from simple Brownian motion. Careful analysis of the data, therefor e, is necessary to identify interesting effects from pure random movem ents. A method was developed to detect temporary confinement in the tr ajectories of membrane proteins that cannot be accounted for by Browni an motion. This analysis was applied to trajectories of two lipid-link ed members of the immunoglobulin superfamily, Thy-1 and a neural cell adhesion molecule (NCAM 125), and the results were compared with those for simulated random walks. Approximately 28% of the trajectories for both proteins exhibited periods of transient confinement, which were <0.07% likely to arise from random movements. In contrast to these res ults, only 1.5% of the simulated trajectories showed confined periods. Transient confinement for both proteins lasted on average 8 s in regi ons that were similar to 280 nm in diameter.