Understanding the delicate balance of forces governing helix or beta-hairpin interactions in transmembrane (TM) proteins is central to understanding membrane structure and function. These membrane constituent interactions play an essential role in determining the structure and function of membrane proteins, and protein interactions in membranes, and thus form the basis for many vital processes, including TM signaling, transport of ions and small molecules, energy transduction, and cell-cell recognition. "Why does a single-pass TM helix or beta-hairpin have specific orientations in membranes?" "What are the roles of hydrogen bonds, close packing, and helix-lipid or beta-hairpin-lipid interactions in helix or beta-hairpin associations in membranes?" "How do these interactions change the membrane structures?" "How do TM domains transmit signals across membranes?" These are important membrane biophysical questions that can be addressed by understanding the delicate balance of forces governing helix or beta-hairpin interactions with/in membranes. In this work, we summarize a series of helix/beta-hairpin restraint potentials that we have developed, and illustrate their applications that begin to address the complicated energetics and molecular mechanisms of these interactions at the atomic level by calculating the potentials of mean force (PMFs) along reaction coordinates relevant to helix/beta-hairpin motions in membranes and dissecting the total PMF into the contributions arising from physically important microscopic forces.
2009 Wiley Periodicals, Inc.