Lecture 7 Flashcards
Most common form of lipid transport?
Within Vesicles
T/F: Soluble proteins are not associated with membranes?
True
How are integral membrane proteins anchored?
Anchored via hydrophobic interactions with the fatty acid chains of the lipid bilayer
Three types of integral membrane proteins?
- Alpha-helices: can have one or multiple helices these span the membrane helices are hydrophobic
- Beta barrel: made up of beta strands
- Amphipathic alpha helix where only one half of the alpha-helix is hydrophobic and the other is hydrophilic
Lipid-Anchored Proteins ?
- Proteins folded in the cytosol/ER lumen and that recieve a PTM that allows them to bind to the PM via a lipid
-Do not enter the PM just covalently linked
Peripheral Membrane Proteins?
-A transmembrane protein that has a motif/domain that interacts through non-covalent binding with another protein that is a soluble protein in the cytosol or lumen
Characteristics of transmembrane proteins?
-Cross the bilayer
-Usually form channels
-3 types
Two types of lipid anchored proteins?
- Those that make covalent bonds with the lipids in the membrane
- Those that make noncovalent bonds with proteins integrated in the membrane(peripheral membrane)
Transmembrane Alpha-helices?
-same as those in the cytosol
-The amino acids that cross the bilayer are typically hydrophobic
-length of the TM helices must match that of the PM
Hydrophobic Amino acids?
-Alanine
-Glycine
-Cysteine
-Leucine
-Phenylalanine
Why does TM alpha-helix need polar residues ?
- If the alpha-helix spans wider than the membrane then polar residues allow it to interact with the environment
- Polar residues allow alpha-helices to interact in the membrane and form channels with a hyrophilic environment
Beta barrels side chains?
Non polar amino acid side chains stick out of the beta barrels and interact with the hydrophobic fatty acids . Pola amino acids form a hydrophilic channel in the middle of the barrel
Number of beta strands?
Determines the size of the channel and the size of the molecule that is able to be transported
Protein modifications only found on cytosolic domains?
-Phosphorylation
-Methylation
-Ubiquitination
-Acetylation
ER lumen vs Cytosol?
Cytosol: Reducing
Lumen : Oxidizing (can have cysteine disulfide bonding)
Channel vs Pump?
Channel:
- Flow with conc. gradient
- No energy
- Regulated opening/closing
Pump:
-FLow against conc. gradient
-Energy
- Regulated by turning ATPase on/off
Channel Proteins?
-Specificity based on pore size
- Regulated flow of ions
-Water-filled channel
Voltage gated K+ channel?
Responsible for neuronal function and heart rhythm
How do channels work?
- Carbonyls from the peptide backbone line the pore
- Ions of the proper size of the hole can exchange their water binding for carbonyls(non covalent)
- Wrong sized molecules will be unable to bind to the carbonyls at all and will be rejected from the channel
Sodium Potassium Pump?
- Sodium is in low abundance in the cytosol. Sodium binds to the ATP pump, ATP is hydrolyzed.
- Conformational change
- Sodium is then released into the cytosol and K+ is picked up
Multidrug Resistance Transporter?
These transporters identify toxins inside the cell and pump them outside of the cell
BAd for chemotherapy
-2 symmetrical ATPase domains that recognize the toxin which binds then ATP hydrolysis and conformational change
Lipid anchored protein acylation?
These proteins bind to the fatty acid chains of the glycolipid or phospholipid
Acylation of cysteine?
-only post translational modification that relies on lipids that is reversible
-Cysteine in any position of the protein is acylated and forms thioester linkage
Acylation involving cysteine or glycine?
-must be the amino acid next to the N-terminus(not ubiquitinated)
-Form an amide linkage with the lipid
-methionine must be cleaved
Lipid anchored protein prenylation?
-Cysteine must be the fourth last amino acid starting from the C-terminus
-Cys - a- a-x-COO-(a hydrophobic AA)
-Not reversible
-Cysteine forms thioester linkage with prenyl group
Three Lipid modifications summary ?
- Cys S-acylation(reversible), thioester linkage any cysteine
- N-terminal acylation: permanent protein binds to fatty acid chains
- Prenylation: thioester bond
All the modifications Cysteine can undergo?
- Disulfide bonding (lumen)
- Ub E1 activating and E2 conjugating enzymes (thioester)
- Lipid modification (thioester, thioether) (Acylation)
- Prenylation (C-a-a-x-COO)
GPI Anchoring ?
-Occurs in the lumen of the ER
- TM helix is removed and the protein is covalently linked to GPI. Region inserted into the PM and one in the lumen of the ER
Integral membrane proteins in the absence of a membrane?
Different 3D strucutre since the hydrophobic regions will go to the middle of the protein
Peripheral and Lipid anchored proteins in the absence of a membrane?
Will have the same structure since they fold into their native state then integrate into the membrane
How would fliiping a transmembrane protein affect it?
Cytosol is a reducing environment, if the protein has disulfide bonding this would cause these bonds to break.
Proteins in the cytosol undergo PTM such as phosphorylation, methylation and acetlyation this could impact the function/structure of the protein
