Simonsen Shane M, Sando Lillian, Rosengren K Johan, Wang Conan K, Colgrave Michelle L, Daly Norelle L, Craik David J
Institute for Molecular Bioscience, University of Queensland, St. Lucia, Brisbane, Queensland 4072, Australia.
J Biol Chem. 2008 Apr 11;283(15):9805-13. doi: 10.1074/jbc.M709303200. Epub 2008 Feb 7.
The cyclotides are stable plant-derived mini-proteins with a topologically circular peptide backbone and a knotted arrangement of three disulfide bonds that form a cyclic cystine knot structural framework. They display a wide range of pharmaceutically important bioactivities, but their natural function is in plant defense as insecticidal agents. To determine the influence of individual residues on structure and activity in the prototypic cyclotide kalata B1, all 23 non-cysteine residues were successively replaced with alanine. The structure was generally tolerant of modification, indicating that the framework is a viable candidate for the stabilization of bioactive peptide epitopes. Remarkably, insecticidal and hemolytic activities were both dependent on a common, well defined cluster of hydrophilic residues on one face of the cyclotide. Interestingly, this cluster is separate from the membrane binding face of the cyclotides. Overall, the mutagenesis data provide an important insight into cyclotide biological activity and suggest that specific self-association, in combination with membrane binding mediates cyclotide bioactivities.
环肽是稳定的植物源微型蛋白质，其肽骨架呈拓扑学环状，且三条二硫键形成纽结排列，构成一个环状胱氨酸结结构框架。它们具有多种重要的药学活性，但其天然功能是作为杀虫剂参与植物防御。为了确定原型环肽卡拉塔B1中单个残基对结构和活性的影响，所有23个非半胱氨酸残基都被依次替换为丙氨酸。结构通常能耐受修饰，这表明该框架是稳定生物活性肽表位的可行候选者。值得注意的是，杀虫活性和溶血活性均依赖于环肽一侧一个常见且明确的亲水性残基簇。有趣的是，该簇与环肽的膜结合面是分开的。总体而言，诱变数据为环肽的生物活性提供了重要见解，并表明特定的自缔合与膜结合共同介导了环肽的生物活性。
