Yang Y S, Mitta G, Chavanieu A, Calas B, Sanchez J F, Roch P, Aumelas A
Centre de Biochimie Structurale, CNRS UMR 5048, INSERM U414, Université Montpellier 1, France.
Biochemistry. 2000 Nov 28;39(47):14436-47. doi: 10.1021/bi0011835.
MGD-1 is a 39-residue defensin-like peptide isolated from the edible Mediterranean mussel, Mytilus galloprovincialis. This peptide is characterized by the presence of four disulfide bonds. We report here its solid-phase synthesis and an easy way to improve the yield of the four native disulfide bonds. Synthetic and native MGD-1 display similar antibacterial activity, suggesting that the hydroxylation of Trp28 observed in native MGD-1 is not involved in the antimicrobial effect. The three-dimensional solution structure of MGD-1 has been established using (1)H NMR and mainly consists of a helical part (Asn7-Ser16) and two antiparallel beta-strands (Arg20-Cys25 and Cys33-Arg37), together giving rise to the common cystine-stabilized alpha-beta motif frequently observed in scorpion toxins. In MGD-1, the cystine-stabilized alpha-beta motif is stabilized by four disulfide bonds (Cys4-Cys25, Cys10-Cys33, Cys14-Cys35, and Cys21-Cys38), instead of by the three disulfide bonds commonly found in arthropod defensins. Except for the Cys21-Cys38 disulfide bond which is solvent-exposed, the three others belong to the particularly hydrophobic core of the highly constrained structure. Moreover, the C4-P5 amide bond in the cis conformation characterizes the MGD-1 structure. MGD-1 and insect defensin A possess similar bactericidal anti-Gram-positive activity, suggesting that the fourth disulfide bond of MGD-1 is not essential for the biological activity. In agreement with the general features of antibacterial peptides, the MGD-1 and defensin A structures display a typical distribution of positively charged and hydrophobic side chains. The positively charged residues of MGD-1 are located in three clusters. For these two defensin peptides isolated from insects and mollusks, it appears that the rather well conserved location of certain positively charged residues and of the large hydrophobic cluster are enough to generate the bactericidal potency and the Gram-positive specificity.
MGD - 1是一种从可食用的地中海贻贝（Mytilus galloprovincialis）中分离出的由39个氨基酸残基组成的防御素样肽。该肽的特征是存在四个二硫键。我们在此报告其固相合成方法以及一种提高四个天然二硫键产率的简便方法。合成的MGD - 1和天然MGD - 1表现出相似的抗菌活性，这表明在天然MGD - 1中观察到的Trp28的羟基化不参与抗菌作用。MGD - 1的三维溶液结构已通过核磁共振氢谱（¹H NMR）确定，主要由一个螺旋部分（Asn7 - Ser16）和两条反平行的β链（Arg20 - Cys25和Cys33 - Arg37）组成，共同形成了在蝎毒素中经常观察到的常见的胱氨酸稳定的α - β基序。在MGD - 1中，胱氨酸稳定的α - β基序由四个二硫键（Cys4 - Cys25、Cys10 - Cys33、Cys14 - Cys35和Cys21 - Cys38）稳定，而不是像节肢动物防御素中常见的三个二硫键。除了溶剂暴露的Cys21 - Cys38二硫键外，其他三个二硫键属于高度受限结构的特别疏水核心。此外，顺式构象的C4 - P5酰胺键是MGD - 1结构的特征。MGD - 1和昆虫防御素A具有相似的抗革兰氏阳性菌杀菌活性，这表明MGD - 1的第四个二硫键对其生物活性不是必需的。与抗菌肽的一般特征一致，MGD - 1和防御素A的结构显示出带正电荷和疏水侧链的典型分布。MGD - 1带正电荷的残基位于三个簇中。对于从昆虫和软体动物中分离出的这两种防御素肽，似乎某些带正电荷残基和大疏水簇的相当保守的位置足以产生杀菌效力和革兰氏阳性特异性。
