Figure 2.

Schemes of the kiss-and-run models of intracellular transport (I–IV) and (A–O). Adapted from Mironov and Beznoussenko [38]. (I) The symmetrical KARM poses that after fusion of the membranes of these two compartments (central image), cargo (black dots inside the ring 2) would diffuse into the lumen of compartment 1. The concentration of cargo would be similar in both compartments. (II) The asymmetric KARM poses that distal compartment 2 is composed of the main part and smaller parts where the cargoes are concentrated. These two parts are connected by thin tubules. Thus, the KARM suggests that the compartments initially fuse, and then for some reason, the tubules undergo fission. For instance, these tubules can be broken easily when lipids from the distal compartment diffuse into them. An additional demand for the asymmetrical KARM is the necessity for a mechanism responsible for the change in the cargoes in such a way that this would induce a greater formation of temporal aggregates by the cargoes. These temporally existing aggregates would be not able to diffuse through the thin tubules backwards. (A–O) Function of the asymmetrical KARM within the Golgi stack (see Movie S1). (A) Formation of the SNARE complex composed of V- and T-SNAREs (brown and magenta lines, left) between the mega-cargo (blue lines) containing cisternal distensions and the rim of the distal cisterna. (B) Fusion between the distensions and the corresponding rim. (C–F) Integration of the distension into the distal cisterna. (G) Elongation of the first cisternae. (H,I) Replacement of the SNAREs and formation of the new SNARE complex composed of another set of SNAREs (red and green line). (J) Fusion of the cargo-containing distension situated within the second cisterna with the rim of the third cisterna containing a pore. (K–O) Additional rounds of fusion/fission processes.