Types of Membrane Proteins Flashcards
What are the 3 types of membrane proteins?
- Integran (intrinsic)
- Peripheral (extrinsic)
- Lipid-linked
How do intrinsic proteins interact with the membrane?
Interact with core of membrane - are tightly bound through interactions with fatty acid chains in the hydrophobic core of the bilayer
Can intrinsic proteins be removed?
Not without breaking the membrane. Can only be extracted (solubilised) by using agents that disrupt the membrane structure e.g. organic solvents (chloroform) or detergents
How do intrinsic proteins span the membrane? How are they distributed?
Span the membrane with single or multiple transmembrane segments
Are asymmetrically distributed across the bilayer
Describe Glycophorin A
- Is a glycoprotein
- Single transmembrane domain
- Sequence passing through membrane is roughly 20 hydrophobic amino acids
Describe extracellular domain of Glycophorin A
Extracellular domain is hydrophilic and glycosylated (extra carbohydrates are added)
Where is Glycophorin A found and why?
In RBCs - enables the to slip through vasculature easily
What type of protein is Glycophorin A?
Intrinsic
What type of protein is Bacteriorhodopsin?
Intrinsic
Describe Bacteriorhodopsin
- 7 transmembrane helices alpha embedded in hydrophobic interior of bilayer
- Bundle of 7 TM helices creates a pore through the membrane
- 20-30 amino acids in an alpha helix to transverse the membrane
How are each of the 7 TM helices linked in Bacteriorhodopsin?
By a short hydrophilic region of the polypeptide chain that is exposed on the extracellular cytosolic side of the membrane
What does the bundle of 7 TM helices through membrane create Bacteriorhodopsin?
Creates hydrophilic core channel - allows transportation of hydrogen ions through
How do lipid-linked proteins interact with the membrane?
Proteins are covalently linked to a lipid which is inserted in the membrane (e.g. covalently attached to fatty acids, have GPI anchor)
How do peripheral proteins interact with the membrane?
Don’t interact with the hydrophobic core of the membrane
Simply interact with hydrophilic heads and sit outside membrane
Where can peripheral proteins be found?
On the outer or inner surface of the bilayer
Can peripheral proteins be removed from the bilayer?
Yes can be separated without damaging the membrane as they are less tightly bound
How do peripheral proteins interact with lipid head groups or with other membrane proteins? How can these interactions be disrupted?
Through ionic interactions
By washing the membrane with high salt solution (high ionic strength). This washes the peripheral membrane proteins off the bilayer in soluble form
What class of proteins do cytoskeletal proteins belong to?
Peripheral proteins
What are spectrin and actin examples of?
Cytoskeletal proteins
What do cytoskeletal proteins form?
Form a scaffold on the cytosolic side of the plasma membrane - this network is attached to the cytosolic domains of the integral membrane proteins
What is job of spectrin?
Forms long filaments
What is job of actin?
Joins spectrin filaments
What is importance of cytoskeleton in RBCs?
Maintaining shape and rigidity of cell and restricting lateral motion of integral membrane proteins
What happens if RBC peripheral proteins are removed?
Cytoskeleton affected
- ‘Ghost’ as lose rigid shape
- Membrane proteins become laterally mobile
What are 2 hereditary diseases that affected cytoskeleton?
Hereditary spherocytosis and elliptocytosis
What is result of these hereditary diseases?
Mutations in genes encoding spectrin or ankyrin which results in abnormally shaped erythrocytes
Erythrocytes are degraded more rapidly by spleen –> ANAEMIA
