Yin Lois M, Lee Soyoung, Mak Jacky S W, Helmy Amr S, Deber Charles M
Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto M5G 1X8.
Protein Pept Lett. 2013 Aug;20(8):843-7. doi: 10.2174/0929866511320080001.
Alginate is a biofilm exopolysaccharide secreted by the opportunistic pathogen Pseudomonas aeruginosa that acts to prevent the diffusion of antibiotics toward the bacterial cell membrane. Cationic antimicrobial peptides (CAPs) have been increasingly recognized as a viable alternative for prospective antimicrobial agents. The D-isomer chiral counterparts of active L-isomer CAPs tend to show slightly greater antimicrobial activities because bacteria lack proteases to hydrolyze the unnatural D-isomers. Using an enantiomeric pair of synthetic CAPs designed in our laboratory (L-4Leu in the sequence KKKKKKALFALWLAFLA-NH2 and its D-analog D-4Leu), we studied the binding and interactions of Lvs. D-isomers of CAPs with alginate using circular dichroism and Raman spectroscopic techniques. We found that the peptide D-4Leu underwent a more rapid structural transition over time from an initial alginate-induced α-helical conformation to a less soluble β-sheet conformation than L-4Leu, indicating that the D-isomer of this peptide has a relatively greater affinity for alginate. Through Raman spectroscopy it was observed that Raman modes at 1297 cm-1 and 1453 cm-1 wavenumbers were found to differ between the spectra obtained from the insoluble complexes formed between L-4Leu vs. D-4Leu and alginate. These modes were tentatively assigned to CH, and CH3 deformation modes, respectively. Our findings reveal previously undetected subtleties in the binding of this diastereomeric pair of peptides in the microenvironment of a biofilm exopolysaccharide, and provide guidelines for future development of antimicrobial peptides.
藻酸盐是由机会致病菌铜绿假单胞菌分泌的一种生物膜胞外多糖，其作用是阻止抗生素向细菌细胞膜扩散。阳离子抗菌肽（CAPs）已越来越被认为是一种可行的新型抗菌剂替代品。活性L-异构体CAPs的D-异构体手性对应物往往表现出略高的抗菌活性，因为细菌缺乏水解非天然D-异构体的蛋白酶。我们使用在实验室设计的一对对映体合成CAPs（序列KKKKKKALFALWLAFLA-NH2中的L-4Leu及其D-类似物D-4Leu），运用圆二色光谱和拉曼光谱技术研究了CAPs的L-异构体与D-异构体和藻酸盐的结合及相互作用。我们发现，与L-4Leu相比，肽D-4Leu随着时间的推移从最初藻酸盐诱导的α-螺旋构象向溶解性较差的β-折叠构象经历了更快的结构转变，这表明该肽的D-异构体对藻酸盐具有相对更高的亲和力。通过拉曼光谱观察到，在L-4Leu与D-4Leu和藻酸盐形成的不溶性复合物的光谱中，1297 cm-1和1453 cm-1波数处的拉曼模式有所不同。这些模式分别初步归属于CH和CH3变形模式。我们的研究结果揭示了在生物膜胞外多糖微环境中这一对非对映体肽结合方面以前未被发现的细微差别，并为抗菌肽的未来开发提供了指导。
