Peptide and protein binding to lipid monolayers studied by FT-IRRA spectroscopy

• A review of the potential of IRRA spectroscopy on monolayers is presented.
• The interaction of peptides and proteins with lipid monolayers is described.
• IRRAS can differentiate between different modes of binding to lipid monolayers.
• Conformational transitions of peptides and proteins upon binding are detected.
• The orientation of peptides and proteins can be studied by angular dependent IRRAS.

Lipid monolayers at the air–water interface represent half of a lipid bilayer and are therefore suitable model systems for studying the binding of peripheral proteins and polypeptides as well as proteins containing hydrophobic membrane anchors to membrane interfaces. Infrared reflection–absorption spectroscopy (IRRAS) of these monolayer films at the air–water interface provides information on the state of the lipid monolayers as well as on the conformational and orientational order of the film constituents. We will review shortly the experimental set-up and the possibilities for obtaining structural information before several applications of the method to lipid–protein monolayers will be described. We will focus on examples where the analysis of the protein and peptide bands for pure monolayers of these compounds are combined with experiments where the same compounds are bound to lipid monolayers. Combination of these experiments leads to detailed information about the conformational properties and the orientation of the molecules at the air-water interface in contrast to being bound to the lipid–water interface. This article is part of a Special Issue entitled: FTIR in membrane proteins and peptide studies.

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