Proteins are kept within the lipid bilayer of a cell by a number of different means depending on their type. Integral proteins extend through the lipid bilayer to make contact with the interior of the cell, where their hydrophobic regions are protected from water. Lipid-bound proteins are held entirely within the lipid bilayer by a glycosylphosphatidylinositol anchor.
Peripheral proteins are not located within the lipid bilayer. Instead, they are bound to the surface of the membrane by interactions with other proteins. Unlike other protein groups, these can be removed without causing any damage to the lipid bilayer. These three groups of proteins can also be bound to specific regions of the lipid bilayer by enzymes.