Protein Targeting: Nucleus Flashcards

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1
Q

What is the size of the nuclear pore complex?

A

125 million Da

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2
Q

What is the diameter of the nuclear pore complex?

A

150 - 200 nm

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3
Q

What is the Nuclear Pore Complex composed of?

A
  • 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
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4
Q

What size of ions, molecules and some proteins does the nuclear pore complex allow to diffuse freely?

A

Up to 60 kDa

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5
Q

What do GTPase Activating Proteins (GAP) do to the G-protein?

A

Switches it to a GDP bound state (OFF)

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6
Q

What do Guanine Nucleotide Exchange Factors (GEFs) do to the G-protein?

A

Switches to a GTP bound state (ON)

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7
Q

What are the TWO characteristics of Nuclear Localisation Signals (NLS)?

A

Neccessary & Sufficient

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8
Q

Which protein recognises NLS?

A

Importins

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9
Q

What forms the Nuclear Import Receptor?

A

A heterodimer of Importin α and Importin β

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10
Q

What is the role of Importin α?

A

Binds to basic NLS sequence

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11
Q

What is the role of Importin β?

A

Mediates transport through the nuclear pore complex

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12
Q

What part of the nuclear pore complex does Importin β and the cargo (cargo complex) interact with?

A

FG-nucleoporins
* Phe (F) and Gly (G) repeats

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13
Q

Diffusion is non-directional so how are nuclear proteins selectively imported to the nucleus where their concentration is higher than in the cytosol?

A
  • Cargo complex is rapidly and selectively disassembled in nucleus
  • Once disassembled from importin, the cargo protein cannot diffuse out of nucleus
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14
Q

Which enzyme regulates the assembly and disassembly of the cargo complex?

A

Ran GTPase

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15
Q

What is the role of Ran GTPase in the NUCLEUS?

A
  • 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
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16
Q

What is the role of Ran GTPase in the CYTOSOL?

A
  • GAP causes Ran to hydolyse GTP and convert to GDP bound state
  • Ran-GDP dissociates from Importin
  • Importin binds to another cargo protein
  • Ran-GDP binds to NTF2 (nuclear transport factor 2) and returns to nucleus
17
Q

Where is Ran-GEF located?

A

Bound to chromatin so remains in the nucleus

18
Q

Where is Ran-GAP located?

A

Associated with the cytoplasmic filaments of the nuclear pore

19
Q

Which amino acid are Nuclear Export Signals (NES) rich in?

A

Leucine

20
Q

What is the Nuclear Export process?

A
  • Exportin-1 forms a complex with Ran-GTP and binds to NES of cargo protein
  • All three proteins diffuse through the NPC
  • At the exit of the pore, Ran-GTP is converted to Ran-GDP and cargo complex is disassociated
  • Cargo protein is released into the cytosol
  • Ran and Exportin-1 return separately to the nucleus
21
Q

What is the major difference between nuclear import and nuclear export in terms of Ran?

A

Ran is part of the cargo complex in nuclear EXPORT

22
Q

What are TWO examples of regulated nuclear transport?

A
  1. T-Cell Activation
  2. Steroid Hormone Receptor activity