Membrane Proteins Flashcards
What percentage of all proteins are membrane-associated?
~30%
What are the two types of membrane proteins?
Integral and peripheral
How are membrane proteins able to be purified?
Using detergents which are amphipathic and dissolve the lipid bilayer
How do detergents separate the proteins from the lipid bilayer?
Detergents act by disintegrating the lipid bilayer while incorporating lipids and proteins in detergent micelles.
Describe how the micelles are formed?
The hydrophobic surface areas of the membrane proteins and the lipid “tails” are buried in the hydrophobic interior of the detergent micellar structures, while hydrophilic parts of the proteins are in contact with the aqueous environment.
What interactions are dissociated by the detergent?
An efficient solubilisation dissociates most lipid-protein and protein-protein interactions, thereby allowing the separation of proteins.
Describe successful solubilisation
A successful solubilisation protocol extracts the membrane protein at a high yield and results in stable protein-detergent complexes (or protein-lipid-detergent complexes) where the protein retains its active conformation.
Describe the conformation of micelles
A few nm in diameter
Molecular weight<100kDa
What is the CMC (Critical Micelle Concentration)?
The concentration at above which monomers will self-assemble into micelles
Not a sharp transition but occurs across a narrow range of concentrations
What can affect the CMC?
Changes to the hydrophilic and hydrophobic groups
What are the 2 types of detergents and surfactants?
Phospholipid like and non-detergent surfactants
Describe phospholipid like detergents
Have a charges headgroup
Single chain
Can destabilise proteins
Describe non-detergent surfactants
Fluorinated surfactants
Amphipols (amphipathic polymers)
