Protein Targeting: Nucleus Flashcards
What is the size of the nuclear pore complex?
125 million Da
What is the diameter of the nuclear pore complex?
150 - 200 nm
What is the Nuclear Pore Complex composed of?
- Octagonal ring structure embedded in the nuclear envelope
- 8 filaments that extend 100nm in nucleoplasm and are joined at their ends to form the nuclear basket
- Cytoplasmic filaments extending into the cytoplasm
What size of ions, molecules and some proteins does the nuclear pore complex allow to diffuse freely?
Up to 60 kDa
What do GTPase Activating Proteins (GAP) do to the G-protein?
Switches it to a GDP bound state (OFF)
What do Guanine Nucleotide Exchange Factors (GEFs) do to the G-protein?
Switches to a GTP bound state (ON)
What are the TWO characteristics of Nuclear Localisation Signals (NLS)?
Neccessary & Sufficient
Which protein recognises NLS?
Importins
What forms the Nuclear Import Receptor?
A heterodimer of Importin α and Importin β
What is the role of Importin α?
Binds to basic NLS sequence
What is the role of Importin β?
Mediates transport through the nuclear pore complex
What part of the nuclear pore complex does Importin β and the cargo (cargo complex) interact with?
FG-nucleoporins
* Phe (F) and Gly (G) repeats
Diffusion is non-directional so how are nuclear proteins selectively imported to the nucleus where their concentration is higher than in the cytosol?
- Cargo complex is rapidly and selectively disassembled in nucleus
- Once disassembled from importin, the cargo protein cannot diffuse out of nucleus
Which enzyme regulates the assembly and disassembly of the cargo complex?
Ran GTPase
What is the role of Ran GTPase in the NUCLEUS?
- GEF keeps Ran in its GTP bound state
- Binding of Ran-GTP to Importin causes dissociation of cargo complex
- Ran-GTP bound to Importin is exported to Cytosol