3.1 Flashcards
Integral protein
-are embedded all the way inside of the cell membrane
-removed with strong chemicals & detergents
Peripheral protein
-membrane associated NOT embedded
-interacts with hydrophilic part of membrane (outside) and polar head groups of lipids
Anchored protein
-Only the hydrophobic tail on the protein is embedded in the membrane
Long chain fatty acids
-palmitoylation on Cys/Ser group
-Myristoylation to amino terminyl Gly
Isoprenoids
Prenylation
GPI
Phosphodiester bond from carboxynl terminus to a GPI (protein covalently bonded to a membrane lipid headgroup)
Amphitropic
-Sometimes associates with the membrane
-is regulated
What motif are integral membrane proteins made of?
-Alpha helices
-Ex: rhodopsin
Membrane-spanning alpha helices
-Made of 20 hydroPHOBIC residues in a row
Hydropathy plot: positive and negative value meanings
-Positive (above line): Hydrophobic
-Negative (below line): Hydrophilic
Membrane-spanning beta barrels
-hydrophobic on the outside and hydrophilic on the inside
-hard to predict–>cannot use hydropathy plot–>instead use sequence comparison
-porins are made of beta barrels
How many amino acids are membrane-spanning alpha and beta barrels made of?
-Alpha: 20 amino acids
-Beta: 7-9 amino acids
What are membrane proteins enriched with?
-Tryptophan and tyrosine residues
-act as interface anchors
Positive inside rule
Positively charged residues are on the CYTOPLASMIC side
Annular lipids 2 primary functions?
- Forms a grease seal around proteins in the membrane
- Stabilizes the protein in the proper orientation in the membrane
Lipid rafts/microdomains
-Signaling
-made of cholesterol and sphingolipids
-contains palmitoylated/myristolated proteins that lets acyl tail insert into lipid bilayer
Caveolin
-Makes the membrane curve
-binds to cholesterol regions of lipid rafts
-has trafficking and signaling functions
What are the 4 domains and functions of caveolin
- Oligomerization: site of dimerization
- Scaffolding: links oligomerization and transmembrane domains
- Transmembrane: 2 helix bundle that transverses the membrane bilayer in cholesterol rich regions
- Membrane attachment-palmitoyl tails insert in membrane
Steps of vesicle fusion
- Vesicle approach: interacts with membrane through adapter proteins
- Zipper: v-SNARE, t-SNARE & SNAP25 form a zipper together which contracts alpha helices and pulls them membranes into proximity
- Membrane hemifusion: Outer leaflets fuse and forms a supermembrane and brings inner leaflets into contact
4.Formation of fusion pore: Vesicular membrane and plasma membrane fuse and pore opens - Release of neurotransmitter to synaptic cleft: Fusion pore widens and releases neurotransmitters
