Mankouri Flashcards
How is membrane integrity maintained?
non-covalent interactions between proteins and lipids
What are the 3 main classes of membrane lipids?
phosphoglycerides, sphingolipids and sterols
Which class of membrane lipid is most common?
phosphoglycerides
How long is the the fatty acid chain of a phospholipid?
6-20Carbon
What factors determine the type of spontaneous aggregation of free lipids?
temperature, length, unsaturation
What molecules are contained in lipid rafts?
cholesterol, glycosphingolipids, sphingomyelin;
GPI anchor and acylated proteins
What processes are lipid rafts involved in?
signalling, endocytosis, cholesterol transport
How are excess lipids stored?
droplets of triacylglycerides and cholesterol esters with proteins targetted for degradation
What are the 3 types of membrane protein?
Integral, peripheral, lipid-anchored
What secondary structure do integral proteins consist of?
alpha-helices
how do peripheral proteins attach to the membrane?
I motif binds polar phospholipid heads- low mobility
what are peripheral proteins used for?
regulate signalling subunits
how are lipid anchored proteins attached to membrane?
covalent bond from N-glycine to acyl of palmitate/mystrate
what does IFABP do?
binds fatty acid precursors in epithelium for transport to sER
what do flippases do?
produce asymmetry between leaflets
what are the classes of flippases?
specific, energy independant, energy dependant inward and outward
where are energy independant flippases located?
ER
What are energy dependant outward flippases know as?
ABC
What are inward flippases know as?
P4P
what are the types of specific flippase?
PE, PC, PS, cholesterol
how are membrane lipids trafficked to their desination?
vesicle integration, transfer proteins or vesicle contact mediated by proteins
what is the N-terminal signal sequence for ER translocation?
N, +, 6-12 hydrophobes, = 16-30 variable total
What does the SRP consist of?
300nt, 6 protein RNP, p54 binds hydrophobes
When does SRP and SPRr hydrolyse GTP?
when bound to translocon for release
How are soluble proteins targetted to the ER?
translation by rER or free ribosome, SRP binds N terminal sequence for stalling, receptor, sec61translocon
what is the structure of the sec61 translocon?
3 proteins, alpha cross linking. aligns to 60S ribosome
what purpose does Sec63.BiP have?
hydrolysis of ATP-ADP binds BiP for unidirectional transport
what are the 2 types of sequence recognised for cotranslational insertion into ER membrane?
Intergral Signal Anchor, Stop-transfer anchor sequence
what type of residues are targeted by the signal petidase?
small neutral residues G/C/A/T @-1, -3
Which types of integral proteins are inserted into the ER with a signal sequence?
1,4,5
which type of integral membrane protein is cleaved for transfer to existing glycosylphosphatidylinositol?
5
Which side of the SA are positive residues?
cytoplasmic
which PTM occurs in ER?
N-glycosylation, oligomerisation, folding, disulphide bond formation
what functions does N-linked Glycosylation have?
folding, targeting, degradative protection, specificity of interactions
What sequence is N-glycosylation bound to?
Asn-X(not Pro)-S/T-
How is N-glycosylation produced?
cotranslational transfer from existing dolichol isoprene lipid by cleavage of pyrophosphate bond
what is the structure of N-glycosylation?
2NAG-9 Mannose- 3 Glucose
how are disulphide bonds formed?
sequential action of PDI, during or immediately after translation. recycled by Ero1,
Which chaperones mediate folding?
PDI/ERp57, PPI, HSP/BiP, calnexin/calrexin for N-glycosylation
Where do O-linked glycosylation and Proteolytic cleavage occur?
Golgi
What structure does O-glycosylation have?
individual sugars to S/T, added using NMP/NDPs.
what sequences are recognised for proteolytic cleavage?
Basic R/K pairs recognised by endoproteases
What type of proteins mediate shedding?
ADAM family
what does shedding produce?
soluble, extracellular/ectoproteins
what types of modification are cytosolic/soluble proteins subject to?
lipid attachment: palmitoylation, prenylation, myristoylation
what consensus sequence is targeted for myristoylation?
(N)-Met-Gly-2-3-4-5
2 not Pro/aromatic/charged
5 S/T/G/C/A/N
what type of modification is myristoylation?
irreversible/covalent but stable, weak for transient signalling and membrane targetting
when does myristoylation occur?
cotranslational, in cytoplasm
Where is palmitoylation added to a protein?
cysteine near c terminus in no concensus sequence. Near TM domain
how stable is palmitoylation?
rapid turnover for signalling and membrane trafficking
what are the 2 types of prenylation?
C15 farnesylation, C20 geranyl geranyl
what sequence does farnesyl target?
Cys-alipathic-alipathic-carboxylate
what sequence does geranyl target?
CC or CXC
when does prenylation occur?
In cytoplasm, PTM
what sequence targets proteins to ER?
KDEL for luminal proteins
what sequence is present on peroxisomal proteins?
SKL(C) also known as PTS1.
Which receptors recognise peroxisomal proteins?
Pex5 in cytoplasm, Pex 14 receptor in membrane
when are peroxisomal proteins folded?
before import
what is the NLS?
7 residues at C terminal of K/R clusters
When are nuclear proteins folded?
after import
what is the mitochondrial targetting sequence?
R/K, 20-50 lacking D/E, hydrophobe
Which receptors are involved in mitochondiral targetting?
TOM20/22 for unfolded cytoplasmic proteins, TOM 40 in outer membrane, TIM44/23/17
what are the 2 destinations of vesicles containing proteins from Golgi?
secretory granules for regulated storage/exocytosis, constitutive exocytosis.
how is the destination of proteins within vesicles dictated?
type of membrane
what is the process of vesicle formation?
adaptor protein-mediated coating, content sorting, bussing, dynamin mediated fission, uncoating, docking
What does dynamin fission require?
GTP or ATP
Which molecules mediate docking of vesicles?
SNAREs e.g. Sec1/Munc-18
what does adaptor protein 1 do?
mediate TGN- endosome movement
what does AP2 do?
interacting with Y motifs for endocytosis with clathrin
where is AP3 localised?
TGN-lysosomes
which type of endocytosis is most common?
clathrin triskelion cage mediated
which additional molecules are required for clathrin-endocytosis?
ephsin and amphipysin for curvature, AP2, dynamin
what is the destination of receptors from endosomes?
Transferrin for iron recycled,
LDL receptor recycled, LDL degraded, cholesterol used
EGFr degraded to turn off
how are receptors recycled from endocytosis?
using RabGTPase
what is caveolin?
protein localised to lipid rafts with cholesterol for pits to mediate endocytosis
how does macropinocytosis act?
cytoskeleton rearrangment into ruffles is coat independant thus low specificity
What length is the STA?
22 residue helix
What are the disulphide bonds of insulin?
1-4,
2-6
3-5
