Houston M E, Kondejewski L H, Karunaratne D N, Gough M, Fidai S, Hodges R S, Hancock R E
Protein Engineering Network of Centres of Excellence, University of Alberta, Edmonton, Canada.
J Pept Res. 1998 Aug;52(2):81-8. doi: 10.1111/j.1399-3011.1998.tb01361.x.
One prominent class of cationic antibacterial peptides comprises the alpha-helical class, which is unstructured in free solution but folds into an amphipathic alpha-helix upon insertion into the membranes of target cells. To investigate the importance of alpha-helicity and its induction on interaction with membranes, a series of peptides was constructed based on a hybrid of moth cecropin (amino acids 1-8) and bee melittin (amino acids 1-18) peptides. The new peptides were predicted to have a high tendency to form alpha-helices or to have preformed alpha-helices by virtue of construction of a lactam bridge between glutamate and lysine side-chains at positions i and i + 4 at various locations along the primary sequence. In two examples where the use of lactam bridge constraints induced and stabilized alpha-helical structure in benign (aqueous buffer) and/or hydrophobic medium, there was a decrease in antibacterial activity relative to the linear counterparts. Thus the preformation of alpha-helix in solution was not necessarily beneficial to antimicrobial activity. In the one case where the lactam bridge did result in increased antibacterial activity (lower minimal inhibitory concentration values) it did not increase alpha-helical content in benign or hydrophobic medium. Broadly speaking, good activity of the peptides against Pseudomonas aeruginosa correlated best (r2 = 0.88) with a helican parameter which was calculated as the induction of alpha-helix in a membrane-mimicking environment divided by the alpha-helix formation under benign conditions. Interestingly, the activity of the lactam bridge peptide constructs correlated in part with alterations in bacterial outer or cytoplasmic membrane permeability.
一类重要的阳离子抗菌肽包括α-螺旋类，这类肽在游离溶液中无结构，但插入靶细胞膜后会折叠成两亲性α-螺旋。为了研究α-螺旋性及其诱导对与膜相互作用的重要性，基于蛾类天蚕素（氨基酸1 - 8）和蜜蜂蜂毒肽（氨基酸1 - 18）的杂交体构建了一系列肽。由于在一级序列的不同位置，在谷氨酸和赖氨酸侧链的i和i + 4位之间构建了内酰胺桥，预测新肽具有形成α-螺旋的高倾向或具有预先形成的α-螺旋。在两个例子中，使用内酰胺桥限制在良性（水性缓冲液）和/或疏水介质中诱导并稳定了α-螺旋结构，但相对于线性对应物，抗菌活性有所降低。因此，溶液中α-螺旋的预先形成不一定有利于抗菌活性。在一个内酰胺桥确实导致抗菌活性增加（最低抑菌浓度值降低）的例子中，它并没有增加良性或疏水介质中的α-螺旋含量。一般来说，肽对铜绿假单胞菌的良好活性与一个螺旋参数最佳相关（r2 = 0.88），该参数计算为在模拟膜环境中α-螺旋的诱导量除以良性条件下α-螺旋的形成量。有趣的是，内酰胺桥肽构建体的活性部分与细菌外膜或细胞质膜通透性的改变相关。
