Membrane Proteins

Membrane proteins can be distinguished from other globular proteins by the high proportion of hydrophobic amino acids they contain.

The nonpolar amino acids are typically arranged in parts of the protein that are embedded in the nonpolar part of the lipid bilayer. These segments are often -helical and can sometimes be identified by plotting the hydrophobicity of the polypeptide sequence.

Membrane proteins are of two general types-integral and peripheral. Integral membrane proteins project through both sides of the lipid bilayer whereas peripheral membrane proteins project through only one side of the lipid bilayer (Figure 10.10). Some membrane proteins are also covalently linked to either carbohydrate or lipid moieties. As can be seen in Table 10.4, the lipid, protein and carbohydrate composition of membranes can vary considerably.

In the erythrocyte membrane, proteins such as ankyrin and the anion channel protein, help to link the membrane to the underlying intracellular backbone.

See also: Table 10.5, Erythrocyte Membrane, Bacteriorhodopsin

INTERNET LINKS:

> 1. Lipid Bilayer Simulation

> 2. Lipid Bilayer

> 3. Lipid Bilayer Models for RasMol