Endocytic vesicle scission by lipid phase boundary forces

The process of endocytosis in budding yeast is not fully understood. It is known that the cell membrane first invaginates and then elongates into a tube. A vesicle forms at the end of this tube and eventually separates. Actin polymerization and membrane-associated proteins are involved in this process. However, the exact roles of these components remain unclear. No prior work had resolved how the vesicle separates from the tube. This gap motivated the development of a quantitative model to explore the scission mechanism. The model focuses on the stage where the membrane has already formed a tube. The protein sheath surrounding the tube is a key factor in the scission process. This study aims to clarify the forces and mechanisms that lead to the separation of the vesicle from the tube.

This study aimed to investigate the mechanisms behind endocytic vesicle scission in budding yeast. The researchers wanted to understand how the vesicle separates from the elongated membrane tube. They focused on the role of the protein sheath that surrounds the tube. The goal was to determine whether the sheath acts by constricting or by causing a phase separation of lipid species. The study also aimed to explore how actin polymerization and myosin I contribute to the scission process. The researchers sought to develop a quantitative model to simulate the scission mechanism. This model would help identify the forces that balance the membrane's elastic resistance. The study aimed to provide a clearer picture of the scission process in yeast endocytosis.

The researchers constructed a quantitative model of the endocytic process in budding yeast. The model begins at the stage where the membrane has formed a tube. The protein sheath surrounding the tube is a central component of the model. The model simulates the scission process by considering the interactions between the sheath and the membrane. The researchers explored two possible mechanisms for scission: constriction of the sheath or phase separation of lipid species. They analyzed how the sheath might act as a filter to separate lipid species. The model also considered the effects of actin polymerization and myosin I on the scission process. The researchers used computational simulations to test the viability of these mechanisms.

The model showed that the protein sheath can act as a filter to cause phase separation of lipid species. This separation leads to a line tension that reduces the interface between the tube and the vesicle. The researchers found that large vesicle size can further decrease the interfacial diameter to a few nanometers. At this scale, thermal fluctuations can fuse the membrane and pinch off the vesicle. The model also demonstrated that actin polymerization and myosin I generate forces that balance the membrane's elastic resistance. These forces are important for the successful scission process. The results suggest that the sheath does not need to constrict to cause scission. Instead, phase separation and line tension can drive the process effectively. The study provides a new perspective on the mechanisms of endocytic vesicle scission.

The study concludes that the protein sheath surrounding the membrane tube can act as a filter to cause phase separation of lipid species. This phase separation generates line tension that reduces the interface between the tube and the vesicle. The researchers found that large vesicle size enhances the reduction of the interfacial diameter. At this scale, thermal fluctuations can lead to membrane fusion and scission. The study also shows that actin polymerization and myosin I generate forces that balance the membrane's elastic resistance. These forces are important for the scission process. The results suggest that the sheath does not need to constrict to cause scission. The findings provide a new understanding of the mechanisms behind endocytic vesicle scission in budding yeast.