Yang Ming, Zhang Chunye, Zhang Michael Z, Zhang Shuping
Department of Veterinary Pathobiology, College of Veterinary Medicine, University of Missouri, Columbia, MO, 65211, USA.
Department of Biomedical Science, College of Veterinary Medicine, University of Missouri, Columbia, MO, 65211, USA.
BMC Microbiol. 2017 Feb 23;17(1):43. doi: 10.1186/s12866-017-0959-9.
Avian β-defensins (AvBD) possess broad-spectrum antimicrobial, LPS neutralizing and chemotactic properties. AvBD-12 is a chemoattractant for avian immune cells and mammalian dendritic cells (JAWSII) - a unique feature that is relevant to the applications of AvBDs as chemotherapeutic agents in mammalian hosts. To identify the structural components essential to various biological functions, we have designed and evaluated seven AvBD analogues.
In the first group of analogues, the three conserved disulfide bridges were eliminated by replacing cysteines with alanine and serine residues, peptide hydrophobicity and charge were increased by changing negatively charged amino acid residues to hydrophobic (AvBD-12A1) or positively charged residues (AvBD-12A2 and AvBD-12A3). All three analogues in this group showed improved antimicrobial activity, though AvBD-12A3, with a net positive charge of +9, hydrophobicity of 40% and a predicted CCR2 binding domain, was the most potent antimicrobial peptide. AvBD-12A3 also retained more than 50% of wild type chemotactic activity. In the second group of analogues (AvBD-12A4 to AvBD-12A6), one to three disulfide bridges were removed via substitution of cysteines with isosteric amino acids. Their antimicrobial activity was compromised and chemotactic activity abolished. The third type of analogue was a hybrid that had the backbone of AvBD-12 and positively charged amino acid residues AvBD-6. The antimicrobial and chemotactic activities of the hybrid resembled that of AvBD-6 and AvBD-12, respectively.
While the net positive charge and charge distribution have a dominating effect on the antimicrobial potency of AvBDs, the three conserved disulfide bridges are essential to the chemotactic property and the maximum antimicrobial activity. Analogue AvBD-12A3 with a high net positive charge, a moderate degree of hydrophobicity and a CCR2-binding domain can serve as a template for the design of novel antimicrobial peptides with chemotactic property and salt resistance.
禽β-防御素（AvBD）具有广谱抗菌、中和脂多糖及趋化特性。AvBD-12是禽免疫细胞和哺乳动物树突状细胞（JAWSII）的趋化因子——这一独特特性与AvBD作为哺乳动物宿主化疗药物的应用相关。为了确定各种生物学功能所必需的结构成分，我们设计并评估了七种AvBD类似物。
在第一组类似物中，通过用丙氨酸和丝氨酸残基取代半胱氨酸消除了三个保守的二硫键，通过将带负电荷的氨基酸残基变为疏水（AvBD-12A1）或带正电荷的残基（AvBD-12A2和AvBD-12A3）增加了肽的疏水性和电荷。该组中的所有三种类似物均表现出改善的抗菌活性，尽管净电荷为+9、疏水性为40%且具有预测的CCR2结合域的AvBD-12A3是最有效的抗菌肽。AvBD-12A3还保留了超过50%的野生型趋化活性。在第二组类似物（AvBD-12A4至AvBD-12A6）中，通过用等排氨基酸取代半胱氨酸去除了一至三个二硫键。它们的抗菌活性受损且趋化活性丧失。第三类类似物是一种杂合体，其具有AvBD-12的主链和带正电荷的氨基酸残基AvBD-6。该杂合体的抗菌和趋化活性分别类似于AvBD-6和AvBD-12。
虽然净正电荷和电荷分布对AvBD的抗菌效力有主导作用，但三个保守的二硫键对于趋化特性和最大抗菌活性至关重要。具有高净正电荷、适度疏水性和CCR2结合域的类似物AvBD-12A3可作为设计具有趋化特性和耐盐性的新型抗菌肽的模板。
