Transmembrane hydrogen-bonded chains

The important role played by solitons in biological transfer remains to be clarified solitons are said to arise from localized disordered regions on, say, a membrane surface in the presence of the transmembrane electric field the local perturbation then tends to spread and to move leading to changes in the orientation of the lipid membrane molecules. The soliton energy is considerably below the energy band gap of a polypeptide chain but may initiate proton transfer in a hydrogen bonded chain in the presence of an electrostatic field. 

Fig. 3. (a) Chemical stmcture of a synthetic cycHc peptide composed of an alternating sequence of D- and L-amino acids. The side chains of the amino acids have been chosen such that the peripheral functional groups of the dat rings are hydrophobic and allow insertion into Hpid bilayers, (b) Proposed stmcture of a self-assembled transmembrane pore comprised of hydrogen bonded cycHc peptides. The channel is stabilized by hydrogen bonds between the peptide backbones of the individual molecules. These synthetic pores have been demonstrated to form ion channels in Hpid bilayers (71). 

The right-handed a-helix (ur) is one of the most common secondary structures. In this conformation, the peptide chain is wound like a screw. Each turn of the screw (the screw axis in shown in orange) covers approximately 3.6 amino acid residues. The pitch of the screw (i. e., the smallest distance between two equivalent points) is 0.54 nm. a-Helices are stabilized by almost linear hydrogen bonds between the NH and CO groups of residues, which are four positions apart from each another in the sequence (indicated by red dots see p. 6). In longer helices, most amino acid residues thus enter into two H bonds. Apolar or amphipathic a-helices with five to seven turns often serve to anchor proteins in biological membranes transmembrane helices see p. 214). 

We envisioned a two-step process [114,115] for the insertion and association of fluorinated transmembrane (TM) helices. First, the hydrophobic TM peptides would partition into micelles or vesicles and form a-helices by main-chain hydrogen bonding. Upon secondary structure formation, one face of the helices would present a highly fluorinated surface. Second, phase separation of fluorinated surfaces within hydrophobic environments would mediate helix-helix interactions, driving bundle formation. 

---