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拟穴青蟹抗脂多糖因子SpALF6抗微生物免疫机制研究
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摘要
抗脂多糖因子(ALFs)是一类具有结合脂多糖(LPS)功能的抗菌肽。鉴于大多数ALFs属于阳离子抗菌肽,且其生物学功能得到了较好的阐明,而阴离子型ALFs生物学功能研究相对较少。本研究从拟穴青蟹(青蟹)中鉴定了一种阴离子型ALF(SpALF6),并通过一系列实验验证了其免疫学功能。SpALF6的cDNA序列全长681bp编码115 AA,其成熟肽和核心结构域pI值分别为6.05和6.79,因此属于阴离子型抗菌肽。SpALF6主要表达于血细胞,弧菌和金黄色葡萄球菌刺激可诱导该基因表达。重组SpALF6能抑制副溶血弧菌、气单胞菌、金黄色葡萄球菌、巨大芽孢杆菌及白色念珠球菌生长。进一步研究发现SpALF6能结合副溶血弧菌、金黄色葡萄球菌、巨大芽孢杆菌及白色念珠球菌的菌体,通过对细菌主要多糖的特异性结合实验证明,SpALF6与菌体的结合活性主要通过与LPS及脂磷壁酸的结合实现,而SpALF6的核心结构域虽能结合多种细菌多糖,但不能抑制上述细菌生长。本研究表明阴离子型抗菌肽SpALF6仍然在青蟹抗菌免疫反应中发挥作用。
Anti-lipopolysaccharide factors(ALFs) are antimicrobial peptides with binding and neutralizing activities to lipopolysaccharide(LPS) in crustaceans. This study identified and characterized a novel ALF homolog(SpALF6) from the mud crab Scylla paramamosain. The complete cDNA of SpALF6 had 681 bp with a 348 bp open reading frame encoding a protein with115 aa. SpALF6 had a low isoelectric point(p I) for the mature peptide and the LPS-binding domain with the values of 6.05 and 6.79, respectively. SpALF6, mainly distributed in hemocytes,could be upregulated by Vibrioparahemolyticus,and Staphylococcus aureus. Recombinant SpALF6 could inhibit the growth of Gram-negative bacteria(Vibrio Parahemolyticus, Aeromonas hydrophila), Gram-postive bacteria(S. aureus and Bacillus megaterium), and a fungus Candida albicans to varying degrees. Further study showed that it could also bind to all the aforementioned microorganisms except Aeromonas hydrophila. Polysaccharide-binding assay conducted by ELISA showed that LPS and LTA are responsible for bacterial cell binding activity of Gram-negative and Gram-postive bacteria, respectively.
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