BCH210H1 Lecture Notes - Lecture 15: Peripheral Membrane Protein, Integral Membrane Protein, Lipid Bilayer
25 May 2018
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Lecture 15: Membrane Protein Properties
Membrane Protein Classes
• Integral (intrinsic, transmembrane)
• Peripheral (extrinsic)
Peripheral Membrane Proteins
• Adhere to membranes or integral membrane
proteins through non-covalent interactions
• Operational definition: removable with mild disruption (high salt or small
change in pH)
Removal of Peripheral Membrane Proteins
• High salt (NaCl) disrupts ionic interactions and
hydrogen bonds by shielding charges
- Amino acid – amino acid
- Amino acid – phospholipid
• pH change disrupts ionic interactions and
hydrogen bonds by
protonating/deprotonating ionisable groups
- Asp, Glu, His, Lys, Arg, (Cys, Tyr)
Amphipathic a-helices have two different faces
• Amphipathic a-helices will just sit on the membrane if
introduced to one
• Non-polar face interacts with lipids
• Polar face interacts with head groups and aqueous
Integral Membrane Proteins
• Completely span the lipid bilayer (i.e. anchored)
• Require harsh conditions to remove from membrane (detergents of organic solvents)
Integral Protein Types
• Type I – single pass NH3+ outside
• Type II – single pass NH3+ inside
• Type III – multi-pass (single protein)
• Type IV – single pass (multiple proteins)
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Document Summary
Peripheral membrane proteins: adhere to membranes or integral membrane proteins through non-covalent interactions, operational definition: removable with mild disruption (high salt or small change in ph) Removal of peripheral membrane proteins: high salt (nacl) disrupts ionic interactions and hydrogen bonds by shielding charges. Amino acid phospholipid: ph change disrupts ionic interactions and hydrogen bonds by protonating/deprotonating ionisable groups. Asp, glu, his, lys, arg, (cys, tyr) Amphipathic a-helices will just sit on the membrane if introduced to one. Polar face interacts with head groups and aqueous. Integral membrane proteins: completely span the lipid bilayer (i. e. anchored, require harsh conditions to remove from membrane (detergents of organic solvents) Integral protein types: type i single pass nh3+ outside, type ii single pass nh3+ inside, type iii multi-pass (single protein, type iv single pass (multiple proteins) Lipid anchored membrane proteins: type v anchored by covalently attached lipid, type vi transmembrane segments and lipid anchors.
