Gramicidin A dimer

Fig. 24. Proposed structure of the Gramicidin A dimer showing the intramolecular and intermolecular hydrogen bonding arrangement. Numbers refer to the amino acid residues Peptide side groups are omitted for clarity.

Fig. 25. Top view of a space-filling model of the proposed Gramicidin A dimer structure, showing the transmembrane channel. [Photograph courtesy of D. A. Haydon]...

The expected channel shown in Figure 12 is of a bimolecular structure. The rigid channel mouth may prohibit the consecutive long alkyl chains from assembling themselves and to prevent lipid molecules from invading the area. The space thus provided may accommodate water molecules to make the domain sufficiently hydrophilic to pass ions. Such a domain would recognize its counterpart located in another lipid layer to make a tail-to-tail dimer of 8, i.e. a symmetric transmembrane channel, as in the case of Gramicidin A dimer. ... 

Fig. 6. Minimum interaction energies of K+ and Na+ with gramicidin A as a function of their position along the channel axis. The top two curves 1911 are calculated according to a model proposed by Gresh et.al. with blocked ethanolamine end chain. The more attractive curves 165-166> are determined using the pair potential method. The gramicidin A dimer ranges from about —14 A to +14 A...

Fig. 2. (A) A view down the channel axis of the gramicidin A dimer. (B) A side view of the gramicidin A dimer channel showing the helical conformation of each monomer.

Figure 2. Schematic models of gramicidin A dimers (A) head-to-head helical dimer (B) tail-to-tail helical dimer (C) antiparallel double-stranded helix (D) parallel double-stranded helix. (Reproduced with permission from reference 301. Copyright 1986 Biophysical Society.)...

Figure 3 Balls and sticks model of the gramicidin A dimer (orthographic projection)...

---