CD spectra of indolicidin antimicrobial peptides suggest turns, not polyproline helix
CD spectra of indolicidin antimicrobial peptides suggest turns, not polyproline helix
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DOI：
10.1021/bi9907936
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发表时间：
1999-09-21
期刊：
影响因子：
2.9
通讯作者：
White, SH
中科院分区：
文献类型：
--
作者：
Ladokhin, AS;Selsted, ME;White, SH
Indolicidin是从牛中性粒细胞的细胞质颗粒中分离的13个残基的抗微生物肽酰胺，其含有5个Trp和3个Pro残基。Falla等，[（1996）J，Biol，Chem.271，19298]提出，基于密切相关的肽（indolicidin甲酯）的圆二色性（CD）光谱，indolicidin形成聚-L-脯氨酸II螺旋。相比之下，我们在各种溶剂中或当结合到胶束和膜时，在天然indolicidin的CD光谱中没有发现聚-L-脯氨酸II螺旋形成的证据[Ladokhin等人（1997）Biophys. J. 72，794]，我们将光谱解释为由无序和/或β-转角结构引起，但注意到由色氨酸残基引起的227 nm处的尖锐负带，其将掩盖聚-L-脯氨酸II螺旋的光谱特征。我们已经重新审视了这个问题，通过CD测量天然indolicidin和它的几个类似物。对于所研究的任何肽，都没有观察到聚-L-脯氨酸螺旋（或α-或3（10）-螺旋）的特征。为了消除与色氨酸相关的伪影，我们合成了indolicidin-L和indolicidin-F，其中所有五个色氨酸分别被亮氨酸或苯丙氨酸取代。转移到膜样环境中后，这些色氨酸-游离肽的CD光谱的变化被发现是一致的形成的p-转角。对于SDS胶束中的天然indolicidin，温度升高导致两个尖锐的带，在227 nm处的负一个和在217 nm处的正一个的耦合减少。这种现象，这是不存在的indolicidin-L变种与单一Leu-Trp取代，是一致的激子分裂所产生的吲哚环的堆叠。已知在水溶液中模型肽中的VI型转变通过顺式-脯氨酸和相邻芳族残基之间的堆积相互作用来促进[Yao等人，（1994）J，Mol. Biol. Biol，243，754]。具有α-Trp（6）-cis-Pro（7）-Trp（8）-型VIa转角的indolicidin的分子建模证明了这种转角构象的可行性，并揭示了伴随两亲性结构的可能性。因此，我们认为，转构象indolicidin的主要结构基序，这些反过来大大提高膜活性。
Indolicidin is a 13-residue antimicrobial peptide-amide isolated from the cytoplasmic granules of bovine neutrophils that contains five Trp and three Pro residues. Falla et al, [(1996) J, Biol, Chem. 271, 19298] suggested that indolicidin forms a poly-L-proline II helix based upon the circular dichroism (CD) spectra of a closely related peptide (indolicidin methyl ester). In contrast, we found no evidence of poly-L-proline II helix formation in the CD spectra of native indolicidin in various solvents or when bound to micelles and membranes [Ladokhin et al. (1997) Biophys. J. 72, 794], We interpreted the spectra as arising from unordered and/or beta-turn structures, but noted a sharp negative band at 227 nm arising from the tryptophan residues that would mask spectral features characteristic of poly-L-proline II helix. We have reexamined this issue by means of CD measurements of native indolicidin and several of its analogues. None of the features characteristic of a poly-L-proline helix (or alpha- or 3(10)-helix) were observed for any of the peptides studied, To eliminate artifacts associated with tryptophan, we synthesized indolicidin-L and indolicidin-F in which all five tryptophans were replaced with leucines or phenylalanines, respectively. The changes in CD spectra of these Trp-free peptides upon transfer into membrane-like environments were found to be consistent with the formation of p-turns. For the native indolicidin in SDS micelles, temperature increases resulted in a coupled diminution of two sharp bands, a negative one at 227 nm and a positive one at 217 nm. This phenomenon, which is absent in indolicidin-L variants with single Leu-Trp substitutions, is consistent with exciton splitting produced by the stacking of indole rings. Type VI turns in model peptides in aqueous solution are known to be promoted by stacking interactions between cis-proline and neighboring aromatic residues [Yao et al, (1994) J, Mol. Biol, 243, 754]. Molecular modeling of indolicidin with a -Trp(6)-cis-Pro(7)-Trp(8)- type VIa turn demonstrated the feasibility of this turn conformation and revealed the possibility of an accompanying amphipathic structure. We therefore suggest that turn conformations are the principal structural motif of indolicidin and that these turns greatly enhance membrane activity.