National Institute of Immunology, New Delhi, India.
PLoS One. 2013 Sep 24;8(9):e75582. doi: 10.1371/journal.pone.0075582. eCollection 2013.
Antimicrobial peptides represent one of the most promising future strategies for combating infections and microbial drug resistance. Tritrpticin is a 13mer tryptophan-rich cationic antimicrobial peptide with a broad spectrum of activity whose application in antimicrobial therapy has been hampered by ambiguity about its biological target and consequently the molecular interactions necessary for its antimicrobial activity. The present study provides clues about the mechanism of action of tritripticin by using a unique monoclonal antibody (mAb) as a 'physiological' structural scaffold. A pool of mAbs were generated against tritrpticin and based on its high affinity and ability to bind tritrpticin analogs, mAb 6C6D7 was selected and characterized further. In a screening of phage displayed random peptides, this antibody was able to identify a novel antimicrobial peptide with low sequence homology to tritrpticin, suggesting that the mAb possessed the physico-chemical characteristics mimicking the natural receptor. Subsequently, thermodynamics and molecular modeling identified a core group of hydrophobic residues in tritrpticin arranged in a distorted's' shaped conformation as critical for antibody binding. Comparison of the mAb induced conformation with the micelle bound structure of tritrpticin reveals how a common motif may be able to interact with multiple classes of biomolecules thus extending the target range of this innate immune peptide. Based on the concurrence between thermodynamic and structural data our results reveal a template that can be used to design novel antimicrobial pharmacophores while simultaneously demonstrating at a more fundamental level the potential of mAbs to act as receptor surrogates.
抗菌肽是对抗感染和微生物耐药性的最有前途的未来策略之一。Tritrpticin 是一种富含色氨酸的 13 mer 阳离子抗菌肽，具有广谱活性，但由于其生物靶标不明确，以及其抗菌活性所需的分子相互作用不明确，其在抗菌治疗中的应用受到了阻碍。本研究通过使用独特的单克隆抗体 (mAb) 作为“生理”结构支架，为 tritrpticin 的作用机制提供了线索。针对 tritrpticin 生成了一组 mAbs，并基于其高亲和力和结合 tritrpticin 类似物的能力，选择并进一步表征了 mAb 6C6D7。在噬菌体展示随机肽的筛选中，该抗体能够识别一种与 tritrpticin 具有低序列同源性的新型抗菌肽，这表明该 mAb 具有模拟天然受体的物理化学特性。随后，热力学和分子建模确定了 tritrpticin 中一组排列成扭曲“s”形构象的疏水性残基为关键的核心基团，对于抗体结合至关重要。将 mAb 诱导的构象与 tritrpticin 的胶束结合结构进行比较，揭示了一个共同的基序如何能够与多种类别的生物分子相互作用，从而扩展这种天然免疫肽的靶标范围。基于热力学和结构数据的一致性，我们的结果揭示了一个模板，可以用于设计新型抗菌药效团，同时在更基本的水平上证明了 mAb 作为受体替代物的潜力。
