Cornet B, Bonmatin J M, Hetru C, Hoffmann J A, Ptak M, Vovelle F
Centre de Biophysique Moléculaire (CNRS), Orléans, France.
Structure. 1995 May 15;3(5):435-48. doi: 10.1016/s0969-2126(01)00177-0.
Insect defensin A is a basic 4 kDa protein secreted by Phormia terranovae larvae in response to bacterial challenges or injuries. Previous biological tests suggest that the bacterial cytoplasmic membrane is the target of defensin A. The structural study of this protein is the first step towards establishing a structure-activity relationship and forms the basis for understanding its antibiotic activity at the molecular level.
We describe a refined model of the three-dimensional structure of defensin A derived from an extensive analysis of 786 inter-proton nuclear Overhauser effects. The backbone fold involves an N-terminal loop and an alpha-helical fragment followed by an antiparallel beta-structure. The helix and the beta-structure are connected by two of the three disulphide bridges present in defensin A, forming a so-called 'cysteine-stabilized alpha beta' (CS alpha beta) motif. The N-terminal loop, which is locally well defined, can occupy different positions with respect to the other moieties of the molecule.
The CS alpha beta motif, which forms the core of the defensin A structure, appears to be a common organization for several families of small proteins with toxic properties. The distribution of amino acid side chains in the protein structure creates several hydrophobic or hydrophilic patches. This leads us to propose that the initial step in the action of positively charged defensin A molecules with cytoplasmic membranes may involve interactions with acidic phospholipids.
昆虫防御素A是一种4 kDa的碱性蛋白，由新大陆绿蝇幼虫在受到细菌攻击或损伤时分泌。先前的生物学测试表明，细菌细胞质膜是防御素A的作用靶点。对该蛋白的结构研究是建立构效关系的第一步，也是在分子水平上理解其抗菌活性的基础。
我们通过对786个质子间核Overhauser效应的广泛分析，描述了防御素A三维结构的优化模型。其主链折叠包括一个N端环和一个α-螺旋片段，随后是一个反平行β-结构。螺旋和β-结构通过防御素A中三个二硫键中的两个相连，形成一个所谓的“半胱氨酸稳定αβ”（CSαβ）基序。局部定义良好的N端环相对于分子的其他部分可以占据不同位置。
构成防御素A结构核心的CSαβ基序，似乎是几个具有毒性的小蛋白家族的共同结构。蛋白质结构中氨基酸侧链的分布产生了几个疏水或亲水区域。这使我们提出，带正电荷的防御素A分子与细胞质膜作用的初始步骤可能涉及与酸性磷脂的相互作用。
