1. Cyclic lipodepsipeptides verlamelin A and B, isolated from entomopathogenic fungus Lecanicillium sp
Kei-Ichi Ishidoh, Hiroshi Kinoshita, Yasuhiro Igarashi, Fumio Ihara, Takuya Nihira J Antibiot (Tokyo). 2014 Jun;67(6):459-63. doi: 10.1038/ja.2014.22. Epub 2014 Apr 2.
Verlamelin and its new derivative (verlamelin B) were isolated from fermentation broth of entomopathogenic fungus Lecanicillium sp. HF627. As the structural elucidation of verlamelin so far was only preliminary, we studied and determined the absolute structure of these two compounds to be cyclo(5S-hydroxytetradecanoic acid-D-alloThr/Ser-D-Ala-L-Pro-L-Gln-D-Tyr-L-Val). This is the first study that precisely analyzed the structure of verlamelin.
2. Molecular mechanics study of ion binding by a cyclic pentapeptide
T E Lynn, J N Kushick Int J Pept Protein Res. 1984 Jun;23(6):601-9. doi: 10.1111/j.1399-3011.1984.tb03132.x.
We have used energy minimization and harmonic analysis to study the structural and thermodynamic changes which occur upon the binding of lithium ions to the cyclic pentapeptide, cyclo-(Gly-L-Pro-Gly-D-Ala-L-Pro) (GPGAP). A number of theoretically stable vacuum configurations of uncomplexed GPGAP were found, one of which is very close to the crystal conformation determined by X-ray diffraction. Stable complexes with lithium were found where the ion binds to the carbonyl oxygen atoms of three residues. Detailed conformational information is presented for both the uncomplexed and the complexed peptide, along with an analysis of the atomic interactions which stabilize the various peptide conformations.
3. Studies on the aggregation and possible channel formation in membranes of a cyclic hexapeptide, cyclo (D-Ala-L-Pro-L-Ala)2
J Ramesh, J K Ghosh, C P Swaminathan, P Ramasamy, A Surolia, S K Sikdar, K R K Easwaran J Pept Res. 2003 Feb;61(2):63-70. doi: 10.1034/j.1399-3011.2003.00033.x.
The interaction of zwitterionic lipid DMPC and DPPC with cyclic hexapeptide, cyclo (D-Ala-L-Pro-L-Ala)2 was studied using circular dichroism (CD) and differential scanning calorimetry (DSC). Preliminary membrane conductance results showed that the peptide has a tendency to form channels inside the lipid bilayer. CD studies indicated that as the lipid/peptide (L/P) ratio (DMPC/peptide) was increased, the magnitude of the negative CD band having a lambda(max) around 200 nm decreased. At a L/P ratio of 210:1, this band disappeared completely, indicating dramatic conformational changes in the peptide on interaction with the lipid bilayer. Reduction of the phase transition temperature and the maximum heat capacity of the lipid bilayer (DPPC) for gel-to-liquid crystalline phase transition indicates a strong interaction of the peptide with the lipid bilayer.
