Curvature of clathrin-coated pits driven by epsin
TL;DR: It is shown here that epsin 1 directly modifies membrane curvature on binding to PtdIns(4,5)P2 in conjunction with clathrin polymerization, and it is proposed that this helix is inserted into one leaflet of the lipid bilayer, inducing curvature.
Abstract: Clathrin-mediated endocytosis involves cargo selection and membrane budding into vesicles with the aid of a protein coat. Formation of invaginated pits on the plasma membrane and subsequent budding of vesicles is an energetically demanding process that involves the cooperation of clathrin with many different proteins. Here we investigate the role of the brain-enriched protein epsin 1 in this process. Epsin is targeted to areas of endocytosis by binding the membrane lipid phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P(2)). We show here that epsin 1 directly modifies membrane curvature on binding to PtdIns(4,5)P(2) in conjunction with clathrin polymerization. We have discovered that formation of an amphipathic alpha-helix in epsin is coupled to PtdIns(4,5)P(2) binding. Mutation of residues on the hydrophobic region of this helix abolishes the ability to curve membranes. We propose that this helix is inserted into one leaflet of the lipid bilayer, inducing curvature. On lipid monolayers epsin alone is sufficient to facilitate the formation of clathrin-coated invaginations.
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TL;DR: ‘Endocytosis’ encompasses several diverse mechanisms by which cells internalize macromolecules and particles into transport vesicles derived from the plasma membrane and must be viewed in a broader context than simple vesicular trafficking.
Abstract: The plasma membrane is the interface between cells and their harsh environment. Uptake of nutrients and all communication among cells and between cells and their environment occurs through this interface. 'Endocytosis' encompasses several diverse mechanisms by which cells internalize macromolecules and particles into transport vesicles derived from the plasma membrane. It controls entry into the cell and has a crucial role in development, the immune response, neurotransmission, intercellular communication, signal transduction, and cellular and organismal homeostasis. As the complexity of molecular interactions governing endocytosis are revealed, it has become increasingly clear that it is tightly coordinated and coupled with overall cell physiology and thus, must be viewed in a broader context than simple vesicular trafficking.
3,709 citations
Cites background from "Curvature of clathrin-coated pits d..."
...Studies with model lipid membranes indicate that epsin, the binding partner of Eps15, has a role in vesicle formation by inserting into the bilayer and generating membrane curvatur...
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TL;DR: What is known about mammalian endocytic mechanisms is reviewed, with focus on the cellular proteins that control these events, and the functional relevance of distinctendocytic pathways is discussed.
Abstract: Endocytic mechanisms control the lipid and protein composition of the plasma membrane, thereby regulating how cells interact with their environments. Here, we review what is known about mammalian endocytic mechanisms, with focus on the cellular proteins that control these events. We discuss the well-studied clathrin-mediated endocytic mechanisms and dissect endocytic pathways that proceed independently of clathrin. These clathrin-independent pathways include the CLIC/GEEC endocytic pathway, arf6-dependent endocytosis, flotillin-dependent endocytosis, macropinocytosis, circular doral ruffles, phagocytosis, and trans-endocytosis. We also critically review the role of caveolae and caveolin1 in endocytosis. We highlight the roles of lipids, membrane curvature-modulating proteins, small G proteins, actin, and dynamin in endocytic pathways. We discuss the functional relevance of distinct endocytic pathways and emphasize the importance of studying these pathways to understand human disease processes.
2,685 citations
TL;DR: Membrane curvature is no longer seen as a passive consequence of cellular activity but an active means to create membrane domains and to organize centres for membrane trafficking.
Abstract: Membrane curvature is no longer seen as a passive consequence of cellular activity but an active means to create membrane domains and to organize centres for membrane trafficking. Curvature can be dynamically modulated by changes in lipid composition, the oligomerization of curvature scaffolding proteins and the reversible insertion of protein regions that act like wedges in membranes. There is an interplay between curvature-generating and curvature-sensing proteins during vesicle budding. This is seen during vesicle budding and in the formation of microenvironments. On a larger scale, membrane curvature is a prime player in growth, division and movement.
2,000 citations
TL;DR: Clathrin-mediated endocytosis is the endocytic portal into cells through which cargo is packaged into vesicles with the aid of a clathrin coat and is fundamental to neurotransmission, signal transduction and the regulation of many plasma membrane activities and is thus essential to higher eukaryotic life.
Abstract: Clathrin-mediated endocytosis is the endocytic portal into cells through which cargo is packaged into vesicles with the aid of a clathrin coat. It is fundamental to neurotransmission, signal transduction and the regulation of many plasma membrane activities and is thus essential to higher eukaryotic life. Morphological stages of vesicle formation are mirrored by progression through various protein modules (complexes). The process involves the formation of a putative FCH domain only (FCHO) initiation complex, which matures through adaptor protein 2 (AP2)-dependent cargo selection, and subsequent coat building, dynamin-mediated scission and finally auxilin- and heat shock cognate 70 (HSC70)-dependent uncoating. Some modules can be used in other pathways, and additions or substitutions confer cell specificity and adaptability.
1,974 citations
Cites background from "Curvature of clathrin-coated pits d..."
...Furthermore, the AP180 amino-terminal homology (ANTH) and epsin N-terminal homology (ENTH) domains are membrane-binding and membrane-bending modules, respectivel...
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TL;DR: This review describes the current experimental tools to study endocytosis of nanomedicines and provides specific examples from recent literature and the authors' own work on endocyTosis of Nanomedicine.
1,819 citations
References
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TL;DR: The method was developed using 12 proteins for which extensive immunochemical analysis has been carried out and subsequently was used to predict antigenic determinants for the following proteins, finding that the prediction success rate depended on averaging group length.
Abstract: A method is presented for locating protein antigenic determinants by analyzing amino acid sequences in order to find the point of greatest local hydrophilicity. This is accomplished by assigning each amino acid a numerical value (hydrophilicity value) and then repetitively averaging these values along the peptide chain. The point of highest local average hydrophilicity is invariably located in, or immediately adjacent to, an antigenic determinant. It was found that the prediction success rate depended on averaging group length, with hexapeptide averages yielding optimal results. The method was developed using 12 proteins for which extensive immunochemical analysis has been carried out and subsequently was used to predict antigenic determinants for the following proteins: hepatitis B surface antigen, influenza hemagglutinins, fowl plague virus hemagglutinin, human histocompatibility antigen HLA-B7, human interferons, Escherichia coli and cholera enterotoxins, ragweed allergens Ra3 and Ra5, and streptococcal M protein. The hepatitis B surface antigen sequence was synthesized by chemical means and was shown to have antigenic activity by radioimmunoassay.
3,767 citations
"Curvature of clathrin-coated pits d..." refers methods in this paper
...Hydrophobicity of the L6 mutants was determined using the Hopp–Woods scal...
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TL;DR: The functional interplay between the coated vesicle machinery and its cargo could ensure sorting fidelity and packaging efficiency and might enable modulation of vesicular trafficking in response to demand.
Abstract: Clathrin-coated vesicles were the first discovered and remain the most extensively characterized transport vesicles. They mediate endocytosis of transmembrane receptors and transport of newly synthesized lysosomal hydrolases from the trans-Golgi network to the lysosome. Cell-free assays for coat assembly, membrane binding, and coated vesicle budding have provided detailed functional and structural information about how the major coat constituents, clathrin and the adaptor protein complexes, interact with each other, with membranes, and with the sorting signals found on cargo molecules. Coat constituents not only serve to shape the budding vesicle, but also play a direct role in the packaging of cargo, suggesting that protein sorting and vesicle budding are functionally integrated. The functional interplay between the coated vesicle machinery and its cargo could ensure sorting fidelity and packaging efficiency and might enable modulation of vesicular trafficking in response to demand.
810 citations
TL;DR: The structure of the NH2-terminal domain of CALM bound to phosphatidylinositol-4,5- bisphosphate [PtdIns( 4,5)P2] via a lysine-rich motif is presented, and it is shown that AP180 may serve to tether clathrin to the membrane simultaneously, and was shown by using purified components and a budding assay on preformed lipid monolayers.
Abstract: Adaptor protein 180 (AP180) and its homolog, clathrin assembly lymphoid myeloid leukemia protein (CALM), are closely related proteins that play important roles in clathrin-mediated endocytosis. Here, we present the structure of the NH2-terminal domain of CALM bound to phosphatidylinositol-4,5- bisphosphate [PtdIns(4,5)P2] via a lysine-rich motif. This motif is found in other proteins predicted to have domains of similar structure (for example, Huntingtin interacting protein 1). The structure is in part similar to the epsin NH2-terminal (ENTH) domain, but epsin lacks the PtdIns(4,5)P2-binding site. Because AP180 could bind to PtdIns(4,5)P2 and clathrin simultaneously, it may serve to tether clathrin to the membrane. This was shown by using purified components and a budding assay on preformed lipid monolayers. In the presence of AP180, clathrin lattices formed on the monolayer. When AP2 was also present, coated pits were formed.
744 citations
TL;DR: Data presented here demonstrate that purified recombinant dynamin binds to a lipid bilayer in a regular pattern to form helical tubes that constrict and vesiculate upon GTP addition, suggesting that dynamin alone is sufficient for the formation of constricted necks of coated pits and supports the hypothesis that dynamIn is the force-generating molecule responsible for membrane fission.
674 citations
"Curvature of clathrin-coated pits d..." refers background in this paper
...Role of helix 0 in membrane curvature Tubulation of liposomes has been observed with a number of protein...
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TL;DR: Results show that amphiphysin binds lipid bilayers, indicate a potential function for amphiphYSin in the changes in bilayer curvature that accompany vesicle budding, and imply a close functional partnership between amphiphisin and dynamin in endocytosis.
Abstract: Amphiphysin, a protein that is highly concentrated in nerve terminals, has been proposed to function as a linker between the clathrin coat and dynamin in the endocytosis of synaptic vesicles. Here, using a cell-free system, we provide direct morphological evidence in support of this hypothesis. Unexpectedly, we also find that amphiphysin-1, like dynamin-1, can transform spherical liposomes into narrow tubules. Moreover, amphiphysin-1 assembles with dynamin-1 into ring-like structures around the tubules and enhances the liposome-fragmenting activity of dynamin-1 in the presence of GTP. These results show that amphiphysin binds lipid bilayers, indicate a potential function for amphiphysin in the changes in bilayer curvature that accompany vesicle budding, and imply a close functional partnership between amphiphysin and dynamin in endocytosis.
652 citations