Trapped In Cristae: Localization And Tracking Of Mitochondrial Membrane-Proteins In Living Cells

Mitochondria are cellular organelles that possess - due to their evolutionary origin - two functionally and biochemically distinct membranes. While the outer membrane encloses the organelle like a sausage casing, the inner mitochondrial membrane extrudes in the interior of mitochondrial. This cristal membrane is probably the site of oxidative phosphorylation (Gilkerson et al, 2003). Yet, the localization of respiratory complexes is not elusive to the cristal membrane (Vogel et al, 2006) as anticipated. On the other hand, cristae junctions were found to separate the two inner membrane compartments implicating a diffusion barrier for membrane proteins (Mannella et al, 2001). To reveal this discrepancy we investigated the spatio-temporal behavior of single respiratory complexes by means of superresolution imaging and single molecule tracking and found different mobilities. ATP synthase displayed the strongest confinement in the cristae when compared to other respiratory complexes. Complementary, outer membrane proteins showed an unrestricted diffusion alongside mitochondria. We thus can explain the patchy appearance of dynamic mitochondria as observed recently (Muster et al, 2010) as to be the result of hindered diffusion within the inner mitochondrial membrane.