Bio202 Lecture 8: Vesicular Transport Part 3 PDF

Lecture 8: Vesicular Transport Part 3 https://doi.org/10.1083/jcb.108.2.389  Today’s agenda - Endocytosis 101 - Clathrin and clathrin-coated vesicles - Types of endocytosis - Autophagy  The endomembrane system...

Lecture 8: Vesicular Transport Part 3 https://doi.org/10.1083/jcb.108.2.389  Today’s agenda - Endocytosis 101 - Clathrin and clathrin-coated vesicles - Types of endocytosis - Autophagy  The endomembrane system Today’s focus! ARROWS secretory pathway endocytic pathway retrieval pathway Figure 15-19  Endocytosis - The process by which cells take in materials through invagination of the plasma membrane. - The material to be ingested is progressively enclosed by a small portion of the plasma membrane, which buds inward and pinches off to form an intracellular endocytic vesicle. - Endocytosed cargo includes receptor-ligand complexes, a spectrum of nutrients and their carriers, extracellular matrix components, cell debris, bacteria, viruses, and, in specialized cases, even other cells. - Cells can use endocytosis to regulate the composition of their plasma membrane. Figure 15-18  The story of endocytosis often starts with clathrin-coated vesicles ARROWS secretory pathway endocytic pathway retrieval pathway  The story of endocytosis often starts with clathrin-coated vesicles EM image showing numerous clathrin-coated vesicles budding from the inner surface of the plasma membrane view – inside of the cell looking up at the plasma membrane Clathrin forms a basket- like network on the cytosolic surface of the membrane Figure 15-20 6  Clathrin-coated vesicles EM images clathrin triskelion https://doi.org/10.1073/pnas.241522198 Figure 15-20  Formation of clathrin-coated vesicles EM images showing stages of clathrin-coated vesicle budding from the inner surface of the plasma membrane Figure 15-20 The mechanism of clathrin-mediated endocytosis Figure 15-21 - Adaptins (adaptor proteins) help select cargo molecules for transport and secure the clathrin coat to the membrane. - Clathrin itself plays no part in choosing specific molecules for transport. The mechanism of clathrin-mediated endocytosis Figure 15-21 Dynamin is required to pinch off the vesicle from the plasma membrane Dynamin and membrane bending proteins are recruited to the neck and help to pinch off the vesicle purified dynamin visualized by EM Dynamin is a large GTPase that assembles into helical structures. GTP hydrolysis by dynamin drives conformational changes in the dynamin helix that constrict the membrane neck. membrane bending proteins assist in the process of pinching off Jenny Hinshaw, NIH  Visualizing clathrin and dynamin dynamics at the plasma membrane Clathrin-RFP Dynamin-GFP Drubin Lab UC Berkeley  Visualizing clathrin and dynamin dynamics at the plasma membrane Clathrin-RFP Clathrin-RFP Dynamin-GFP Dynamin-GFP Drubin Lab UC Berkeley  Analysis of a dynamin mutant This dynamin mutant cannot hydrolyze GTP and, therefore, cannot pinch off the vesicle! Figure 15-21  Types of endocytosis pinocytosis “cellular drinking” receptor-mediated endocytosis phagocytosis “cellular eating”  Types of endocytosis pinocytosis “cellular drinking” - involves the ingestion of fluid and molecules via small pinocytic vesicles (