β-defensins (BDs) are small-molecule cysteine-rich cationic antimicrobial peptides that play an important role in innate immunity against microbial invasion. In this study, a β-defensin (SmBD) was identified and characterized from turbot (Scophthalmus maximus). SmBD has an open reading frame containing 192 bp and encodes a protein of 63 amino acids. It has a predicted signal peptide consisting of 20 amino acids and a mature peptide with six conserved cysteine residues forming three disulfide bonds (C1- C5, C2-C4 and C3-C6). The 3D structure prediction shows an N-terminal α-helix and three reverse parallel β-folds. SmBD showed high sequence identity (70.45% - 95.24%) with β-defensin 2 group members from other teleost species. SmBD had the highest expression in skin of healthy turbot and was significantly up-regulated in mucosal tissues (skin, gill, intestine) after bacteria challenge. SmBD showed antibacterial activity against Vibrio anguillarum, Edwardsiella tarda, Escherichia coli and Streptococcus iniae, and inhibitory effect on the formation of bacterial biofilms. SmBD changed bacterial membrane permeability and affected bacterial morphology, as shown in fluorescence microscopy and scanning electron microscopy analyses, respectively, which indicated that SmBD might exercise antibacterial behaviors via “membrane-attack” mechanism.

β-防御素（BDs）是富含小分子半胱氨酸的阳离子抗菌肽，在抵抗微生物入侵的先天免疫中起着重要作用。在这项研究中，从大菱turbo（Scophthalmus maximus）中鉴定并鉴定了一种β-防御素（SmBD））。SmBD具有一个包含192 bp的开放阅读框，编码63个氨基酸的蛋白质。它具有一个由20个氨基酸组成的预测信号肽和一个带有六个保守半胱氨酸残基的成熟肽，形成三个二硫键（C1-C5，C2-C4和C3-C6）。3D结构预测显示N末端为α螺旋和三个反向平行的β折叠。SmBD与来自其他硬骨鱼类的β-防御素2组成员表现出高度的序列同一性（70.45％-95.24％）。在细菌攻击后，SmBD在健康大菱expression的皮肤中表达最高，并且在粘膜组织（皮肤，腮，肠）中明显上调。SmBD对鳗弧菌，塔氏爱德华氏菌，大肠杆菌和链球菌具有抗菌活性。，以及对细菌生物膜形成的抑制作用。如荧光显微镜和扫描电子显微镜分析所示，SmBD改变了细菌膜的通透性并影响了细菌的形态，这表明SmBD可能通过“膜​​攻击”机制行使抗菌行为。