Rebuffat S, Goulard C, Hlimi S, Bodo B
Laboratoire de Chimie des Substances Naturelles, Muséum National d'Histoire Naturelle, Paris, France.
J Pept Sci. 2000 Oct;6(10):519-33. doi: 10.1002/1099-1387(200010)6:10<519::AID-PSC273>3.0.CO;2-6.
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.
假康宁素KL III和KL VI是两种天然的十肽，它们都含有（Xaa-Yaa-Aib-Pro）基序，且具有不寻常的C末端。除了经典的以β-氨基醇为C末端的肽菌素外，它们是通过高效反相HPLC从真菌假康宁木霉中分离得到的。通过结合使用正离子LSI-MS和二维同核及异核NMR（包括COSY、TOCSY、ROESY、13C异核单量子相关（HSQC）和异核多键相关（HMBC））确定了C末端的氨基酸序列和化学结构。假康宁素KL III和KL VI的C末端分别为-Pro-NH2和环（Aib-L-Proal）（Proal，脯氨醛），而不是通常在肽菌素中作为C末端残基的氨基醇之一。这种主链修饰在此首次针对肽菌素抗生素进行描述。不寻常的环（Aib-L-Proal）C末端可能是十个氨基酸前体的最后两个Aib和Pro残基通过Proal中间体进行分子内环化的结果。根据ROESY数据、3JNHCalphaH偶合和酰胺质子温度系数值，推断出这两种肽都具有由1<--4型-C=O...H-N-氢键稳定的二级结构。首次在含有三个重复（Xaa-Yaa-Aib-Pro）基序的14肽菌素（Segalas G等人，生物聚合物，1999；50：71-85）中描述的（Xaa-Yaa-Aib-Pro）β-转角带状螺旋似乎在这两种缩短的修饰肽中得以保留。因此，β-转角带状结构似乎由单个（Xaa-Yaa-Aib-Pro）基序引发，且不受C末端修饰的影响。然而，假康宁素KL III和KL VI的膜及抗生素特性表明肽链的缩短和环化都具有不利影响。
