Determining the occurrence of a 3(10)-helix and an alpha-helix in two different segments of a lipopeptaibol antibiotic using TOAC, a nitroxide spin-labeled C(alpha)-tetrasubstituted alpha-aminoacid.
Trichogin GA IV is a 11-residue lipopeptaibol antibiotic exhibiting membrane modifying properties. We synthesized step-by-step by solution methods three trichogin analogues, each with a double Aib (alpha-aminoisobutyric acid)-->TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) replacement. The strict similarity in the conformational propensities of Aib and TOAC allowed us to exploit these analogues in a detailed investigation of the conformation of this lipopeptaibol in different organic solvents and in a membrane-mimetic environment using in particular the double spin labeling ESR technique. We conclude that the secondary structure in solution remains essentially unchanged if compared to that previously found in the crystal state for trichogin. More specifically, the N-terminal region of the peptide folds in a 3(10)-helix, while the central and C-terminal regions are mainly alpha-helical. An additional, significant proof for the modest plasticity of the trichogin structure was obtained by an X-ray diffraction analysis of the nOct-[TOAC4,8, Leu-OMe11] analogue. For the three analogues permeability measurements revealed membrane-modifying properties comparable to those of natural trichogin.
Monaco
V
V
Biopolymer Research Center, CNR, Department of Organic Chemistry, University of Padova, Italy.
Formaggio
F
F
Crisma
M
M
Toniolo
C
C
Hanson
P
P
Millhauser
G
G
George
C
C
Deschamps
J R
JR
Flippen-Anderson
J L
JL
D000621:Aminoisobutyric Acids / Q000737:chemistry; D000900:Anti-Bacterial Agents / Q000737:chemistry*; D002463:Cell Membrane Permeability / Q000187:drug effects; D003497:Cyclic N-Oxides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D006020:Glycopeptides; D006860:Hydrogen Bonding; D055666:Lipopeptides; D008081:Liposomes / Q000378:metabolism; D008958:Models, Molecular; D010455:Peptides / Q000138:chemical synthesis; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
D000621:Aminoisobutyric Acids; D000900:Anti-Bacterial Agents; D003497:Cyclic N-Oxides; D005456:Fluorescent Dyes; D006020:Glycopeptides; D055666:Lipopeptides; D008081:Liposomes; D010455:Peptides; C116419:trichogin GA IV; C100049:2-aminoisobutyric acid; C037109:2,2,6,6-tetramethylpiperidine-N-oxide-4-amino-4-carboxylic acid