期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：12
页码：E1423-E1432
DOI：10.1073/pnas.1418491112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceBiological cells are engaged in an incessant uptake of macromolecules for nutrition and inter- and intracellular communication; this entails significant local bending of the plasma membrane and formation of cargo-carrying vesicles executed by a designated set of membrane-deforming proteins. The energetic cost incurred in forming vesicles is directly related to the stressed state of the membrane and, hence, that of the cell. In this study, we reveal a protein-induced "snap-through instability" that offsets tension and drives vesicle growth during clathrin-mediated endocytosis, the main pathway for the transport of macromolecules into cells. Because these proteins (actin and BAR proteins) are involved in other interfacial rearrangements in cells, the predicted instability could be at play in cells at-large. Clathrin-mediated endocytosis (CME) is a key pathway for transporting cargo into cells via membrane vesicles; it plays an integral role in nutrient import, signal transduction, neurotransmission, and cellular entry of pathogens and drug-carrying nanoparticles. Because CME entails substantial local remodeling of the plasma membrane, the presence of membrane tension offers resistance to bending and hence, vesicle formation. Experiments show that in such high-tension conditions, actin dynamics is required to carry out CME successfully. In this study, we build on these pioneering experimental studies to provide fundamental mechanistic insights into the roles of two key endocytic proteins--namely, actin and BAR proteins--in driving vesicle formation in high membrane tension environment. Our study reveals an actin force-induced "snap-through instability" that triggers a rapid shape transition from a shallow invagination to a highly invaginated tubular structure. We show that the association of BAR proteins stabilizes vesicles and induces a milder instability. In addition, we present a rather counterintuitive role of BAR depolymerization in regulating the shape evolution of vesicles. We show that the dissociation of BAR proteins, supported by actin-BAR synergy, leads to considerable elongation and squeezing of vesicles. Going beyond the membrane geometry, we put forth a stress-based perspective for the onset of vesicle scission and predict the shapes and composition of detached vesicles. We present the snap-through transition and the high in-plane stress as possible explanations for the intriguing direct transformation of broad and shallow invaginations into detached vesicles in BAR mutant yeast cells.
