Lecture 11 Flashcards
Gated Transport
Occurs between nucleus and cytosol through nuclear pore complexes (bidirectional)
Transmembrane Transport
Membrane protein translocators directly transport specific proteins from cytosol across an organelle membrane (unidirectional)
Vesicular Transport
Membrane-enclosed transport intermediates move proteins between various compartments via vesicles (bidirectional)
Protein sorting signals
Simple stretch of amino acids; may be localized in N or C terminus or within protein; necessary and sufficient for protein targeting - recognized by complementary receptors
What is unique about the signal sequence for import into the nucleus?
It is Lys-Arg rich
Nuclear Pore Complexes (NPCs)
Composed of nucleoporins arranged in octagonal “basketlike” symmetry with aqueous pores and fibrils (FG repeats) - passive diffusion or facilitated transport
Nuclear Localization Signals (NLS)
Sorting signals that direct molecules to nucleus; rich in lysine/arginine, located at many different sites on protein and result in selective import
Nuclear Import Receptors (NIRs)
Receptors that recognize a subset of cargo proteins; they bind to NLS n protein and NPC proteins present on fibrils at FG repeats; release cargo inside of nucleus
What is unique about the fibrils located on NPCs?
They contain FG (phenylalanine-glycine) repeats on which NIRs can bind
Nuclear Export Signals (NES)
Molecules that direct proteins out of the nucleus
Nuclear Export Receptors (NERs)
Receptors complementary to the NES which bind to cargo in nucleus and NPC proteins and facilitate transport until cargo released into cytoplasm
What drives nuclear transport in the appropriate direction?
Gradient of Ran conformational states
What causes Ran-GDP to be cytosolic?
Interaction with GAP (also causes hydrolysis to GDP form)
What causes Ran-GTP to be nuclear?
Interaction with GEF
What is the result of Ran-GTP binding to import receptor and cargo?
Release of cargo; Ran-GTP and the import receptor leave the nucleus
