Figure 2.

Mean square displacement of proteins diffusing in the outer membrane of E. coli. Each curve is an average curve over many single-molecule experiments tracking individual molecules. The short-time linear region is used to estimate the molecule's diffusion coefficient. (a) Time dependence of the mean square displacement of the cobalamin receptor BtuB (closed squares) and the outer membrane pore OmpF (closed circles). Both molecules were imaged using a low concentration of antibodies labelled with Alexa Fluor 555. (b) Expanded view of the OmpF curve from (a) compared with the mean square displacement measured for anti-BtuB immobilized on the coverglass as a standard for the precision of the measurement. Reprinted with permission from Spector et al. [10].