protein sorting- signal-based targeting Flashcards
includes:
ER, mitchondria, chloroplast, peroxisome, nucleus
ER co-translational translocation signal seq
N term signal seq, bound by SRP
ER co-translational translocation receptor
SRP receptor, has A and B subunits
ER co-translational translocation translocation channel
translocon, has Sec61A component
ER co-translational translocation energy
No ATP needed, energy from chain elongation
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
ER post-translational translocation signal seq
N term signal seq
ER post-translational translocation receptor
none
ER post-translational translocation channel
translocon
ER post-translational translocation energy
Sec63 complex (member of Hsc70 family of molec chaperones (BiP))
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
mitochondrial matrix seq
amphipathic N term helix
mitochondrial matrix receptor
import receptor (Tom 20/22), inner membrane receptor (Tim 44)
mitochondrial matrix channel
general import pore (Tom 40), inner mem (Tim23/17)
mitochondrial matrix energy
from within mitochondria, ATP hydrolysis by Hsc70
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
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
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)
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
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
nucleus signal seq
NLS, NES
nucleus channel
nuclear pore complex (NPC), FG repeats provide HPB
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)
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)
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
