Intro to membrane proteins

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  • Created by: lridgeway
  • Created on: 03-11-20 10:55

Membrane environment

The membrane enviroment is very unusual and is a restriction environement (2D). Membrane lipids form a permeability barrier (they don't stop everything but slow and prevent many) and therefore compartments are established. 

Specifc proteins mediate nearly all other membrane functions and transport chemivals and information across the membrane. 

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How do proteins associate with membranes?

The oily fatty interior of the membrane rasies issues for protein sturcture as does the hydrophillic head as this puts pressue on interactions proteins can make. 

Integral membrane proteins - embed fully into membrane and usually trasnverse it 

Peripheral membrane proteins - bulk of surface within aqueous environment around membrane. These are not embedded they associate with the surface via other proteins or the head group of lipids

Lipid-anchor proteins - Bulk outside but attched to membrane via lipid anchors. These are essentially peripheral proteins

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How tightly do proteins associate?

The ease at which a membrane protein can be dissociated indicates how closely assocaited to the membrane it is. Proteins need isolating in order to be able to view them and work out thier function.

Some can be solubilized by mild means such as using a solution of high ionic strength, others require a detergent (specifically chemically synthesized) or an organic solvent (often denature protein so need to be careful). They can be classified as either peripheral or integral based on this difference. Peripheral ones can be more easily solubilized than integral ones. 

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Peripheral and integral membrane proteins

Integral proteins interact extensively with the membrane so in order to remove them a agent that competes are the interactions will work. This is what organic solvents and dtergents do. 

Peripheral proteins are bound by electrostatic interactions and hydrogen bonds with lipid head groups (except for lipid anchors). The interactions are easily disrupted by change in pH or by addition of salts. They are also bound to surfaces of integral proteins on the cytoplasmic or extracellular sides of the membrane. Others are anchored to the bilayer by a covalently attached hydrophobic chain. 

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