Saravanan Rathi, Bhattacharjya Surajit
School of Biological Sciences, Division of Structural and Computational Biology, Nanyang Technological University, Singapore 637551, Singapore.
Biochim Biophys Acta. 2011 Jan;1808(1):369-81. doi: 10.1016/j.bbamem.2010.10.001. Epub 2010 Oct 8.
The broad spectrum of antibacterial activities of host defense cationic antimicrobial peptides (AMPs) arises from their ability to perturb membrane integrity of the microbes. The mechanisms are often thought to require assembly of AMPs on the membrane surface to form pores. However, three dimensional structures in the oligomeric form of AMPs in the context of lipid membranes are largely limited. Here, we demonstrate that a 22-residue antimicrobial peptide, termed VK22, derived from fowlicidin-1, a cathelicidin family of AMP from chicken oligomerizes into a predominantly tetrameric state in zwitterionic dodecylphosphocholine (DPC) micelles. An ensemble of NMR structures of VK22 determined in 200mM perdeuterated DPC, from 755 NOE constrains including 19 inter-helical NOEs, had revealed an assembly of four helices arranged in anti-parallel fashion. Hydrogen bonds, C(α)H-O=C types, and van der Waals interactions among the helical sub-units appear to be involved in the stabilization of the quaternary structures. The central region of the barrel shaped tetrameric bundle is non-polar with clusters of aromatic residues, whereas all the cationic residues are positioned at the termini. Paramagnetic spin labeled NMR experiments indicated that the tetrameric structure is embedded into micelles such that the non-polar region located inside the lipid acyl chains. Structure and micelle localization of a monomeric version, obtained from substitution of two Tyr residues with Ala, of the peptide is also compared. The mutated peptide VK22AA has been found be localized at the surface of the micelles. The tetrameric structure of VK22 delineates a small water pore that can be larger in the higher order oligomers. As these results provide structural insights, at atomic resolution, into the oligomeric states of a helical AMP in lipid environment, the structural details may be further utilized for the design of novel self-assembled membrane protein mimics.
宿主防御阳离子抗菌肽（AMPs）的广谱抗菌活性源于它们破坏微生物膜完整性的能力。其机制通常被认为需要抗菌肽在膜表面组装形成孔道。然而，在脂质膜环境中抗菌肽寡聚体形式的三维结构在很大程度上受到限制。在此，我们证明了一种由鸡源cathelicidin家族的fowlicidin-1衍生而来的22个残基的抗菌肽VK22，在两性离子十二烷基磷酸胆碱（DPC）胶束中主要寡聚成四聚体状态。在200mM全氘代DPC中测定的VK22的一组NMR结构，来自755个NOE约束，包括19个螺旋间NOE，揭示了四个螺旋以反平行方式排列的组装体。螺旋亚基之间的氢键、C（α）H - O = C类型以及范德华相互作用似乎参与了四级结构的稳定。桶状四聚体束的中心区域是非极性的，有芳香族残基簇，而所有阳离子残基都位于末端。顺磁自旋标记NMR实验表明，四聚体结构嵌入胶束中，使得非极性区域位于脂质酰链内部。还比较了该肽的单体形式（通过将两个Tyr残基替换为Ala获得）的结构和胶束定位。已发现突变肽VK22AA定位于胶束表面。VK22的四聚体结构描绘了一个小的水孔，在更高阶的寡聚体中可能更大。由于这些结果在原子分辨率上提供了关于螺旋抗菌肽在脂质环境中寡聚状态的结构见解，这些结构细节可能会进一步用于设计新型自组装膜蛋白模拟物。
