llecture 4 Flashcards
what does the signal peptidase recognise
small neutral side chains
what drives the movement across the ER
Sec63+BiP also HSP
ahs peptide binding domain and ATPases domain.
what does Sec63 promote
BiP-ATP hydrolysis. makes change so it can bind to polypeptide chain.
how does type 1 integral membrane protein insert into the membrane
hydrophobic TM domain enter translocon. the stop-transfer anchor sequence take place. once embedded translocation continues.
N-terminal ER sequence is cleaved. C-terminal is cytosilic
how is type 2 membrane protein inserted
located internally. SRP recognises it. TM domain is signal sequence. embeds in ER bilayer.
c-terminal is luminal
describe type 3 membrane insertion protein
same as type 2. positive charge placement is different on C-terminal side so C-terminus is in cytosol. has internal signal sequence can’t’ cleave.
give and example for type1,2,3
1= LDL receptor, insulin receptor, growth hormone receptor
2= transferin receptor
3= cytochrome 450
what do tail anchored membrane proteins depend on
Get3(ATPase) binds to c-terminal of protein. Get1/Get2 receptor recruits. ATP hydrolysis. c-terminus release and embedded
describe the topology of type 5 membrane protein
alpha helix direct, anchor or stop transfer protein to ER. N-terminus can be cytosolic or luminal.
what attaches phospholipid anchors to proteins
glycosylphosphatidylinositol which is a amphipathic molecule
what recognises the AA sequence near N-terminus
transamidase
what does transamidase do
cleave stop anchor sequence. transfer ER luminal part to GPI membrane anchor.
what modifications take place in the ER
N-linked glycosylation
disulphide bond formation
aid folding
oligomer formation
what modifications take place in the golgi
o-linked glycosylation
proteolytic processing
what modification takes place at the cell surface
protein shedding
describe how n-linked glycosylation takes place
glycan+ nitrogen atom of asparagine= oligosaccharide- nascent polypeptide in lumen of ER- cleave pyrophosphate bond between dolichol-glycan molecule. processing reactions. glucose and mannose removed. n-linked glycan- ER chaperones+ 3 glucose residues on core. help fold. 3 glucose removed. if fold fail + 3 glucose.
how do disulfide bonds form in secretory proteins
oxidising environment. link sulfhydryl groups. 2 cysteine residues. not in cytosolic protein. protein disulphide isomerase present. reducing agent. Ero 1- carries s-s bond to give to PDI. oxidise PDI. disulphides exchange on protein.
describe protein oligomer formation
spikes form hemagglutinin protein. trimers formed in ER of host cell. =precursor HA0.post translational.
what do o-glycosyltransferases do
+ activated sugars to O-atom on serine and threonine residues
describe the proteolytic processing
inactive to functional. basic AA pairs recognised by endoproteases in golgi.
what does proteolytic shedding do
=soluble membrane proteins.
give an example of proteolytic shedding
ADAM family remove ectodomains of membrane proteins
what sequence does the KDEL-R recognise
KDEL
which retention signal reaches the plasma membrane
Kir6.2 RKR
what mediates golgi targeting
transmembrane domains hydrophobic. 17-25 AA long
what are cytosolic motifs
golgi targeting signal. 4-10 AA. charge residue interact with cytosolic factor and machinery
give an example of a cytosolic motif and what it does
SDYQRL. tyrosine interact with adaptor complexes. AP2 u2 binds to tyrosine motif. captures TGN46 at plasma membrane goes back to golgi network
what is AP1-5
clathrin associated adaptor protein complex. recognise tyrosine and dileucine base signal
what is GGA1-3
located in golgi. trafficks cargo from TGN to endosome system
describe the clathrin triskelion
3x clathrin heavy chains 3x light
adaptor complexes bind to clathrin help in tis self assembly and recruitment.
what do vesicle coats bind to
sorting signals
what does sec24 recognise
di-acidic motif at ER COPII
what is dynamin GTPase
neck of vesicle- polymerise- energy GTP- change- neck stretches- pinches off
what happens when GTP hydrolysis doesn’t take place
the clathrin bud cannot pinch off
what drives the depolymerisation of the clathrin coat
HSP70
what disrupts mitochondrial targeting
mutation of hydrophobic and hydrophillic residues on either side of the helix
what do import receptors recognise
Tom 20 and 22 both on outside of mitochondrial membrane
what keeps proteins in disaggregated state
HSP70 AND 90
what is Tom 40
import pore for unfolded chain. passive driving force comes from matrix.
what does Tom 40 associate with
Tim23 and 17 which HSP70 interacts with via Tim44 when entering . both drive the polypeptide into the matrix
describe the mitochondrial inner membrane protein pathway A
Tom20/22-N-terminal sequence-Tom40-inner membraneTim23/17- sequence cleave- hydrophobic stop transfer sequence-translocation stop-insert membrane
describe pathway B
matrix targeted-internal hydrophobic domain-Oxa1 recognises it.
describe pathway c
internal sequence-Tom70/22-trnaslocated-Tim22/54-transfer-Tim9/10-chaperones-stop folding-Tim22/54 insert hydrophobic regions into membrane.
how are outer mitochondrial membrane proteins arranged
beta barrel-all interact with Tom40 and go to sorting and assembly complex
what does SAM consist of
3 proteins
how were nuclear localisation signals discovered
by large T-antigen of simian virus 40
give an example of peroxisome targeting
PTS1+ Pex5-Pex14 in membrane peroxisome-catalase released to interior- through Pex2/10/12-folded proteins translocated
how are peroxisomes generated
Pex3 and 16-ER membrane-recruit Pex19-bud off-empty peroxisome
