Protein–lipid interaction is the influence of membrane proteins on the lipid physical state or vice versa. The questions which are relevant to understanding of the structure and function of the membrane are: 1) Do intrinsic membrane proteins bind tightly to lipids (see annular lipid shell), and what is the nature of the layer of lipids adjacent to the protein? 2) Do membrane proteins have long-range effects on the order or dynamics of membrane lipids? 3) How do the lipids influence the structure and/or function of membrane proteins? 4) How do peripheral membrane proteins which bind to the layer surface interact with lipids and influence their behavior?