protein sorting- signal-based targeting

Question 1

includes:

Answer 1

ER, mitchondria, chloroplast, peroxisome, nucleus

Question 2

ER co-translational translocation signal seq

Answer 2

N term signal seq, bound by SRP

Question 3

ER co-translational translocation receptor

Answer 3

SRP receptor, has A and B subunits

Question 4

ER co-translational translocation translocation channel

Answer 4

translocon, has Sec61A component

Question 5

ER co-translational translocation energy

Answer 5

No ATP needed, energy from chain elongation

Question 6

ER co-translational translocation mech

Answer 6

signal seq -> SRP -> delivers to SRP receptor -> interactions strengthened by GTP, complex disassembled and polypep moves into translocon when hydrolyzed to GDP, signal peptidase cuts off signal seq, extrude the rest into lumen

Question 7

ER post-translational translocation signal seq

Answer 7

N term signal seq

Question 8

ER post-translational translocation receptor

Answer 8

none

Question 9

ER post-translational translocation channel

Answer 9

translocon

Question 10

ER post-translational translocation energy

Answer 10

Sec63 complex (member of Hsc70 family of molec chaperones (BiP))

Question 11

ER post-translational translocation mech

Answer 11

polypep already made, N term seq cleaved off, BiP•ATP becomes BiP•ADP by Sec63, BiP•ADP binds to polypep, prevents from slipping out of ER, more BiP•ADP added on as it slides further into lumen, released and folds

Question 12

mitochondrial matrix seq

Answer 12

amphipathic N term helix

Question 13

mitochondrial matrix receptor

Answer 13

import receptor (Tom 20/22), inner membrane receptor (Tim 44)

Question 14

mitochondrial matrix channel

Answer 14

general import pore (Tom 40), inner mem (Tim23/17)

Question 15

mitochondrial matrix energy

Answer 15

from within mitochondria, ATP hydrolysis by Hsc70

Question 16

mitochondrial matrix mech

Answer 16

precursor protein remains unfolded by Hsc70, binds to import receptor, transferred to general import pore, translocates into inner mem at contact sites, matrix processing protease cleaves N term seq, folded by chaperonin

Question 17

inner mitochondria membrane pathways (3 but will only talk about 2)

Answer 17

1) stop transfer seq, matrix targeting seq (sim to ER mem type 1 mech)
2) Oxa-1 targeting seq, matrix targeting seq

Question 18

mitochondrial intermembrane space pathways (2)

Answer 18

1) intermem-space target seq, matrix targeting seq; sim to type 1 mech except the embedded mem protein is cleaved by the the mem protease, protein floats away and binds to heme cofactor
2) only has intermem-space target seq, delivered directly through general import pore, uses Erv1/Mia40 (disulfide bond formation)

Question 19

chloroplast thylakoids plastocyanin

Answer 19

N term stromal-import seq cleaved off by stromal protease, reveals thylakoid-targeting seq, SRP-dep pathway (sim to bacterial version of SRP pathway), cleaved when it gets inside thylakoid

Question 20

chloroplast thylakoids metal binding protein

Answer 20

N term stromal-import seq cleaved off by stromal protease, reveals thylakoid-targeting seq (has Arg res for recognition), pH dep pathway, metal ions added, pH gradient needed for transport into thylakoid, cleaved when it gets inside thylakoid

Question 21

nucleus signal seq

Answer 21

NLS, NES

Question 22

nucleus channel

Answer 22

nuclear pore complex (NPC), FG repeats provide HPB

Question 23

nucleus import mech

Answer 23

importin binds to NLS of cargo, diffuses through NPC, Ran•GTP binds to importin, importin undergoes confirmational change, NLS/cargo released, importin/Ran•GTP transported to cytoplasm, Ran•GTP -> Ran•GDP with GAP (cytoplasm), importin released, Ran•GDP goes back into nucleoplasm, Ran•GDP -> Ran•GTP with GEF (nucleoplasm)

Question 24

nucleus export mech

Answer 24

exportin binds to NES of cargo, binds to Ran•GTP, diffuses through NPC, Ran•GTP -> Ran•GDP with GAP (cytoplasm), complex dissociates, cargo stays in cytoplasm, exportin and Ran•GDP go back into nucleoplasm, Ran•GDP -> Ran•GTP with GEF (nucleoplasm)

Question 25

mRNP (messenger ribonuclear protein complex) exporter

Answer 25

nuclear export factor 1 (NXF1)/nuclear export transporter 1 (NXT1) complex binds to mRNPs in nucleus, NXF1/NXT1 acts as nuclear export factor, diffuses through NPC, RNA helicase (Dbp5) in cytoplasm removes mRNA (powered by ATP), NXF1/NXT1 recycled back into nucleus with nuclear import mech