Fig. 2
From: Employing aromatic tuning to modulate output from two-component signaling circuits
Schematic summary of the evidence supporting the affinity of amphipathic aromatic residues for polar/hydrophobic interfaces. a Mixing peptides consisting of a poly-Ala-Leu core of different lengths flanked by Trp residues (WALP peptides) with synthetic bilayers of different thicknesses demonstrates the affinity of the Trp residues for the polar/hydrophobic interfaces [14, 15]. When the distance between the Trp residues was sufficiently shorter than the distance between the polar/hydrophobic interfaces, the lipids adopted an inverted hexagonal (HII) phase to accommodate interactions between the Trp residues and the interfacial regions (left panel). When the distance between the flanking aromatic residues was increased so that it matched the distance between the interfacial regions, lamellar phases were observed (center panel). As the distance between Trp residues was increased, the acyl chains became more ordered suggesting a slight expansion of the bilayer to accommodate these “larger” peptides (right panel). b Glycosylation-mapping analysis employs a Lep model protein with two TM helices [18]. Segments to be analyzed are inserted at TM2 and a glycosylation-accepting site is positioned between 6 and 11 residues away from the lumenal boundary of TM2. Glycosylation-accepting sites shown in green are distal enough to become glycosylated while those in red are not. Proximity of an accepting site to the active site of oligosaccharyltransferase (OST) correlated with the extent of glycosylation. Therefore, repositioning of TM2 will change these relative positions and hence the extent of glycosylation. c Calculation of minimum glycosylation distance (MGD). MGD simply indicates the number of residues required for half-maximal glycosylation. Repositioning of TM2 into the membrane will increase MGD, while outward displacements of TM2 result in a reduction of MGD. Previous changes in MGD have demonstrated that moving Trp residues about the lumenal end of TM2 resulted in bidirectional, i.e., into and out of the membrane, displacement of the TM helix [19]