Membrane Proteins Flashcards
Evidence for proteins in membranes (functional and biochemical)
Functional:
Facilitated diffusion
Ion gradients maintained
Specific cell responses
Biochemical:
Membrane fractionation + gel electrophoresis
Freeze fracture
SDS page of erythrocyte
SDS coats with negative charge
Smaller molecules move further towards +ve end
Spectrin largest
Actin smallest
Freeze fracture
Using knife, plane of fracture occurs through bilayer separating it out.
Low angle shadowing allows view (electrons build up on proteins and where proteins were)
Mobility of proteins in bilayer (3)
Conformational chnage
Lateral
Rotational
NO FLIP FLOP - LOCKED IN
What restricts protein mobility
Aggregates of protein
Lipid mediated effects (lipid rafts)*
Tethering to cytoskeleton or peripheral
Interaction with other cells
*BUT Proteins do tend to separate into fluid regions/cholesterol poor regions
Peripheral proteins
Bound to surface by electrostatic/hydrogen bonds
Be seperated using pH or ionic strength (salt)
Integral proteins behaviour
Interact with hydrophobic domains of bilayer
Cannot be removed with pH/ionic strength
Removed by agents that compete for hydrophobic (non polar) interactions (eg detergents/solvents)
What sort of amino acid groups would you find in membrane
Small, hydrophobic, polar (uncharged)
How do you see if a protein is a membrane protein
Hydropathy plots
Shows hydrophobic regions above line and hydrophillic below
What is membrane protein topology
Orientation of protein within bilayer
Carbohydrate always faces outside
N terminal is usually un cytosol
What change is important that underpins protein function and differentiates it from lipid?
Conformational change - allows 3D structure to change and facilitate transport (ligand gated channels, carrier etc)
