As opposed to soluble proteins, the surfaces of membrane proteins like Baceriorhodopsin are in close contact to the surrounding lipids.

This requires the presence of hydrophobic patches on the surface of the protein (green), facing the hydrophobic membrane core. The only hydrophilic surface residues (red) are located within the headgroup layers.

Such features are often realized by amphiphatic secondary structures, e.g. helices or sheets with just one hydrophobic face.