Two unprecedented natural Aib-peptides with the (Xaa-Yaa-Aib-Pro) motif and an unusual C-terminus: structures, membrane-modifying and antibacterial properties of pseudokonins KL III and KL VI from the fungus Trichoderma pseudokoningii.
Pseudokonins KL III and KL VI are two natural ten-residue peptides, which both contain the (Xaa-Yaa-Aib-Pro) motif and exhibit an unusual C-terminus. They have been isolated from the fungus Trichoderma pseudokoningii by intensive reversed-phase HPLC, beside peptaibols classically C-ended by a beta-amino alcohol. The amino acid sequences and the chemical structures of the C-ends have been determined by the combined use of positive ion LSI-MS and two-dimensional homo- and heteronuclear NMR, including COSY, TOCSY, ROESY, 13C heteronuclear single quantum correlation (HSQC) and heteronuclear multiple bond correlation (HMBC). Instead of one of the amino alcohols usually found as C-terminal residue in peptaibols, pseudokonins KL III and KL VI are characterized by -Pro-NH2 and cyclo-(Aib-L-Proal) (Proal, prolinal), respectively. Such backbone modifications are described here for the first time for peptaibol antibiotics. The unusual cyclo-(Aib-L-Proal) C-terminus is probably the result of an intramolecular cyclization of the two last Aib and Pro residues of a ten-amino acid precursor, via a Proal intermediate. A secondary structure stabilized by -C=O...H-N-hydrogen bonds of the 1<--4 type has been deduced for both peptides from ROESY data, 3JNHCalphaH couplings and amide proton temperature coefficient values. The (Xaa-Yaa-Aib-Pro) beta-bend ribbon spiral, which has been described for the first time in the case of a 14-residue peptaibol containing three repetitive (Xaa-Yaa-Aib-Pro) motifs (Segalas G et al. Biopolymers 1999; 50: 71-85) appears to be maintained in the two shortened modified peptides. The beta-bend ribbon structure thus appears to be initiated by a single (Xaa-Yaa-Aib-Pro) motif and unaffected by the C-terminal modifications. However, the membrane and antibiotic properties of pseudokonins KL III and KL VI, point to the unfavourable effect of both shortening and cyclization of the peptide chain.
Rebuffat
S
S
Laboratoire de Chimie des Substances Naturelles, Muséum National d'Histoire Naturelle, Paris, France. rebuffat@mnhn.fr
Goulard
C
C
Hlimi
S
S
Bodo
B
B
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D005656:Fungal Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy; D008826:Microbial Sensitivity Tests; D010455:Peptides / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology*; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D014242:Trichoderma / Q000737:chemistry*
D000900:Anti-Bacterial Agents; D005656:Fungal Proteins; D008081:Liposomes; D010455:Peptides; C421703:pseudokonin KL III; C421704:pseudokonin KL VI