Section: New Results

Modeling and estimation of protein release and diffusion in TIRFM

Participants : Antoine Basset, Charles Kervrann, Patrick Bouthemy.

We have pursued our work on membrane dynamics, still following a local approach in space and time. We have proposed a new model to account for the full behavior of cargo transmembrane proteins during the vesicle fusion to the plasma membrane at the end of the exocytosis process (see Fig. 5 ). It combines release and diffusion steps. The former is represented by an exponential decay to account for a continuous release of the proteins from the vesicle to the plasma membrane. We can relax the usual point source assumption,  and we name our model the “Small-extent Source with Exponential Decay release” (SSED). An iterative minimization method is used to estimate simultaneously both biophysical parameters, i.e., the release rate and the diffusion coefficient, for every active vesicle detected in the total internal reference fluorescence microscopy (TIRFM) image sequence. Quantitative evaluation has demonstrated the efficiency of the method, which has also allowed us to exhibit differences in the behaviors of Transferrin receptor (TfR) and Langerin proteins.

Collaborators: Jean Salamero (UMR 144 CNRS-Institut Curie, PICT-IBiSA),

                          Jérôme Boulanger (UMR 144 CNRS-Institut Curie).

Figure 5. Left: Fusing vesicle (frame in red) in a TIRFM (UMR 144 CNRS-Institut Curie, PICT-IBiSA) sequence (frame 325, 50ms/frame). Right: Zoom-in view of the temporal evolution of the fusing vesicle.