Energetics of side-chain snorkeling in transmembrane helices probed by nonproteinogenic amino acids

Significance Membrane proteins are central players in all cells, and their structure and function are under intense study. However, we still lack a detailed understanding of the process whereby they are integrated into biological membranes. Most membrane proteins are integrated cotranslationally into the membrane bilayer. Although the energetics that drive membrane protein integration are known in outline, detailed studies are difficult because the naturally occurring amino acids represent only a limited set of side-chain chemistries. Here we use synthetic, nonproteinogenic amino acids engineered into a transmembrane segment to systematically probe the energetics of membrane insertion in a way not possible with the set of natural amino acids.