Figure 2.

Mechanisms of SNARE proteins in membrane fusion. The process begins with the docking of a vesicle to the target membrane. The vesicle and target membranes come into close proximity, facilitated via specific interactions between SNARE proteins (PDB ID 2C5J) present on both membranes. SNARE proteins on the vesicle membrane (v-SNAREs) and the target membrane (t-SNAREs) interact with each other, forming a highly stable and tightly coiled complex known as the SNARE complex. This complex consists of a four-helix bundle, with the v-SNARE and t-SNAREs contributing two helices each. The SNARE complex undergoes a process called “zippering”. This involves the progressive and tight association of the four helices, pulling the vesicle and target membranes closer together. The energy released during this zippering process helps overcome the repulsive forces between the membranes, leading to their fusion. As the SNARE complex completes its zippering, the lipid bilayers of the vesicle and target membranes merge, allowing the contents of the vesicle to be released into the target compartment. This process is accompanied by the mixing of transmembrane proteins and lipids, facilitating the exchange of molecules between the two compartments. After membrane fusion, the SNARE complex disassembles with the help of ATPase NSF (N-ethylmaleimide-sensitive factor) and its cofactor SNAPs (soluble NSF attachment proteins). This disassembly step prepares the SNARE proteins for subsequent rounds of membrane fusion. Created with BioRender.