The Composition and Architecture of Membranes:- Peripheral Membrane Proteins Are Easily Solubilized

Membrane proteins may be divided operationally into two groups (Fig. 11–6). Integral proteins are very firmly associated with the membrane, removable only by agents that interfere with hydrophobic interactions, such as detergents, organic solvents, or denaturants. Peripheral proteins associate with the membrane through electrostatic interactions and hydrogen bonding with the hydrophilic domains of integral proteins and with the polar head groups of membrane lipids. They can be released by relatively mild treatments that interfere with electrostatic interactions or break hydrogen bonds; a commonly used agent is carbonate at high pH. Peripheral proteins may serve as regulators of membrane-bound enzymes or may limit the mobility of integral proteins by tethering them to intracellular structures.

FIGURE 11–6 Peripheral and integral proteins. Membrane proteins can be operationally distinguished by the conditions required to re lease them from the membrane. Most peripheral proteins are released by changes in pH or ionic strength, removal of Ca²⁺ by a chelating agent, or addition of urea or carbonate. Integral proteins are ex tractable with detergents, which disrupt the hydrophobic interactions with the lipid bilayer and form micelle-like clusters around individual protein molecules. Integral proteins covalently attached to a mem brane lipid, such as a glycosyl phosphatidylinositol (GPI; see Fig. 11–14), can be released by treatment with phospholipase C.

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مواضيع ذات صلة

Solute Transport across Membranes:- Transporters Can Be Grouped into Superfamilies Based on Their Structures

Solute Transport across Membranes:- Passive Transport Is Facilitated by Membrane Proteins

Membrane Dynamics:- Membrane Fusion Is Central to Many Biological Processes

The Composition and Architecture of Membranes:- Sphingolipids and Cholesterol Cluster Together in Membrane Rafts

The Composition and Architecture of Membranes:- A Lipid Bilayer Is the Basic Structural Element of Membranes

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins:- Cooperative Ligand Binding Can Be Described

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins:- Hemoglobin Undergoes a Structural Change on Binding Oxygen

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins:- Hemoglobin Subunits Are Structurally Similar to Myoglobin

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins: -Oxygen Is Transported in Blood by Hemoglobin

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins:- Protein Structure Affects How Ligands Bind

Membrane Dynamics:- Transbilayer Movement of Lipids Requires Catalysis

The Composition and Architecture of Membranes:- Lipids and Proteins Diffuse Laterally in the Bilayer