nuclear import and export

Question 1

structure of nuclear pore complex

Answer 1

pore complex has stable components including a plug and a spoke complex with 8 fold symmetry around the plug. Asymmetrically distributed in nuclear membrane. Laterally, 3 layers, each has a different function. Membrane layer attached to nuclear membrane. Scaffolding layer that give curvature to membrane. Barrier layer are fairly amorphus and are the functional unit. have FG repeats

Question 2

role of nucleoporins (Nups)

Answer 2

functional unit of transport capable of bidirectional transport through the nucleus

Question 3

role of karyopherins

Answer 3

aka importins/exportins/tranportins. Mediate transport to/from nucleus. Directly interact with FG Nups or cargo. Receptor molecule recognizes specific carge for entry, helps regulate nuclear entry

Question 4

role of Ran

Answer 4

energy dependent step, Ran in its GTP binding state binds to receptor and causes the displacement of cargo.

Question 5

basic mechanism of nuclear import and export

Answer 5

cargo binds to alpha subunit, which binds to beta subunit, and passes into the nucleus. Import Ran-GTP binds in the nucleus to separate the cargo and receptor, which passed through alone. Export receptor cargo complex binds to Ran-GTP, tri-complex goes out together, GTPase hydrolyzes the GTP, exports seperate.

Question 6

signals for transport

Answer 6

usually exposed linear AA seq. contains multiple basic or hydrophobic residues.

Question 7

regulation

Answer 7

entropy barrier created by Nups, the presence of Ran, the interaction of cargo transporters and Nups, and cargo modification

Question 8

defects causing disease

Answer 8

diseases occur when proteins are mislocalized, either by selectivity barrier compromise, or mutaions