INTD5000, REVIEW, Lectures C7-C8 Professor Eileen M. Lafer Tel#: 7-3764 Email: Lafer@biochem.uthscsa.edu Office: Room 415B THE SECRETORY AND ENDOCYTIC PATHWAYS Reading: Chapters 12 and 13 from Alberts et al., Molecular Biology of the Cell

THREE TYPES OF PROTEIN MOVEMENT BETWEEN COMPARTMENTS Gated transport: nuclear pore complex, cytosol<-> nucleus Transmembrane transport: protein translocators (proteins usually unfold), cytosol-> ER, cytosol-> mitochondria Vesicular transport: membrane-enclosed transport, ER <-> golgi post-golgi traffic Review Alberts

THE BIOSYNTHETIC-SECRETORY AND ENDOCYTIC PATHWAYS Alberts

PROTEIN SYTHTHESIS IN THE ROUGH ER: Transmembrane Transport Post-Translational Modification Alberts

OLIGOSACCHARIDE CHAINS ARE PROCESSED AS THEY MOVE THROUGH THE VARIOUS GOLGI APPARATUS

VESICULAR TRANSPORT Transport vesicles bud from one compartment and fuse with another, carrying material from the lumen of the donor compartment, and depositing it in the lumen of the target compartment. Alberts

VESICULAR TRANSPORT IS MEDIATED BY COATED VESICLES How do transport vesicles form? Alberts et al., Molecular Biology of the Cell-3rd edition

THERE ARE VARIOUS TYPES OF COATED VESICLES Clathrin-endocytosis and golgi to endosome. CopI-intra-golgi and golgi to plasma membrane. CopII-ER to golgi Alberts

DIFFERENT COATS ARE USED IN DIFFERENT TRAFFICKING PATHWAYS Alberts

THE STRUCTURE OF A CLATHRIN COAT Kirchhausen, Harrison, Walz, Fotin

MOVIE: STRUCTURE OF THE SEC13/31 COPII COAT a, Views of the cage along its two-fold (left panel), three-fold (centre panel) and four-fold (right panel) axes of symmetry. The surface of the cage is coloured from blue (nearest) to yellow (farthest) according to its distance from the centre of the volume. Scale bar, 500 Å. b, The asymmetric unit and vertex of the cuboctahedral Sec13/31 lattice. Structural features are numbered 1–6. The proposed Sec13/31 heterotetramer arrangement is indicated by the green lines for Sec13 and blue lines for Sec31. c, Close-up of a cage vertex. Vertex–vertex (v–v) and edge–vertex (e–v) interactions are indicated. FROM: Stegg et al., Nature 439: 234-239, 2006.

The Assembly and Disassembly of a Clathrin Coat

ASSEMBLY AND BUDDING OF COPII and COPI COATED VESICLES Figure 2 Coat assembly and vesicle budding. (a) COPII coat assembly is initiated by the ER resident, Sec12, which serves as a guanine nucleotide exchange factor (GEF) for the small GTPase, Sar1 (1). GTP binding by Sar1 exposes an amphipathic α-helix that facilitates association with the ER membrane. Membrane-associated Sar1 recruits the Sec23-24 heterodimer (2), and this complex interacts with cargo proteins via specific sorting signals (3). The Sar1-Sec23-Sec24 complex then recruits the Sec13-31 heterotetramer (4), which is thought to polymerize the coat and drive membrane deformation to yield a COPII vesicle, shown in thin section (Schekman & Orci 1996). (b) COPI coat assembly is similar in that coat recruitment is initiated by GDP-GTP exchange on Arf1, mediated by the ARF GEF, Gea1 (1). Membrane-bound Arf1 then recruits the preassembled coatomer complex, which contains seven subunits: the α/β'/ε complex and the β/γ/δ/ζ complex (2). The COPI coatomer complex likely contains multiple cargo recognition sites on separate subunits that mediate recruitment of cargo proteins (3). Ultimately, the coat is polymerized by an unknown mechanism, and membrane curvature may facilitate the recruitment of an Arf GTPase-activating protein (ARF GAP), stimulating GTP hydrolysis by Arf and subsequent dissociation from the membrane (4). A purified COPI vesicle is shown in thin section (Schekman & Orci 1996). FROM: Lee et al., Annu. Rev. Cell Dev. Biol. 20:87-123, 2004.