protein sorting- signal-based targeting Flashcards Preview

BICD 110 > protein sorting- signal-based targeting > Flashcards

Flashcards in protein sorting- signal-based targeting Deck (25):
1

includes:

ER, mitchondria, chloroplast, peroxisome, nucleus

2

ER co-translational translocation signal seq

N term signal seq, bound by SRP

3

ER co-translational translocation receptor

SRP receptor, has A and B subunits

4

ER co-translational translocation translocation channel

translocon, has Sec61A component

5

ER co-translational translocation energy

No ATP needed, energy from chain elongation

6

ER co-translational translocation mech

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

7

ER post-translational translocation signal seq

N term signal seq

8

ER post-translational translocation receptor

none

9

ER post-translational translocation channel

translocon

10

ER post-translational translocation energy

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

11

ER post-translational translocation mech

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

12

mitochondrial matrix seq

amphipathic N term helix

13

mitochondrial matrix receptor

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

14

mitochondrial matrix channel

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

15

mitochondrial matrix energy

from within mitochondria, ATP hydrolysis by Hsc70

16

mitochondrial matrix mech

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

17

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

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

18

mitochondrial intermembrane space pathways (2)

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)

19

chloroplast thylakoids plastocyanin

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

20

chloroplast thylakoids metal binding protein

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

21

nucleus signal seq

NLS, NES

22

nucleus channel

nuclear pore complex (NPC), FG repeats provide HPB

23

nucleus import mech

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)

24

nucleus export mech

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)

25

mRNP (messenger ribonuclear protein complex) exporter

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