U-shaped caveolin-1 conformations are tightly regulated by hydrogen bonds with lipids.

The structure and dynamics of a truncated (residues 82-136) caveolin-1 (Cav1) construct having a helix-break-helix motif are explored by both all-atom free energy and molecular dynamics (MD) simulations in an explicit bilayer membrane. Two stable Cav1 conformations with small (LB-Cav1) and large hinge angles (RB-Cav1) between two helices are identified although their relative free energy cannot be reliably estimated due to the sampling issues. RB-Cav1s contain one or two lipids residing between the helices that are hydrogen bonded (h-bonded) to both helices in a multidentate fashion. LB-Cav1s show the helices with mono-dentate lipid h-bond interactions or multidentate interactions limited to a single helix at most. The two conformational states of Cav1 remain their initial state during 2-µs MD simulation, suggesting that there is a significant hidden barrier (other than the insertion depth of Cav1 and its hinge angle) and the Cav1 conformational states are tightly regulated by the h-bonds between Cav1 and lipids along with the associated lipid rearrangement during the course of Cav1 conformational changes. © 2019 Wiley Periodicals, Inc.

Methods for studying transmembrane peptides in bicelles: consequences of hydrophobic mismatch and peptide sequence.

We have shown that bicelles prepared from dilauryl phosphatidylcholine (DLPC) and dipalmitoyl phosphatidylcholine (DPPC) align in a magnetic field under conditions similar to the more common dimyristoyl phosphatidylcholine (DMPC) bicelles. In addition, a model transmembrane peptide, P16, with a hydrophobic stretch of 24 A, and specific alanine-d(3) labels, was incorporated into all of the different bicelles. The long-chain phospholipid (DLPC, DMPC, or DPPC) remained unperturbed upon incorporation of the peptide while the quadrupolar splitting of the short-chain phospholipid along the bicelle rim increased by varying degrees in the different bicelle systems. The change in quadrupolar splitting of the short-chain phospholipids was attributed to changes in either fluidity of the planar region of the bicelle or differences in overall lipid packing. When the hydrophobic stretch of the bilayer was 22.8 (DMPC) or 26.3 A (DPPC), the peptide tilt was found to be transmembrane (33-35 degrees with respect to the bicelle normal). When the hydrophobic stretch of the bilayer was 19.5 A (DLPC), the peptide quadrupolar splittings suggested a loss of transmembrane orientation. When tryptophan was incorporated in the middle of the transmembrane region, the transmembrane orientation was also lost.