title: Purification and characterization of a novel defensin from the salivary glands of the black fly, Simulium bannaense.
abstract: BACKGROUND
  Black flies (Diptera: Simuliidae) are haematophagous insects that can cause allergic reactions and act as vectors of pathogens. Although their saliva has been thought to contain a diverse array of physiologically active molecules, little information is available on antimicrobial factors in black fly salivary glands, especially no defensins have been reported so far.
  
  
  METHODS
  A novel cationic defensin designated SibaDef was purified using reverse phase high-performance liquid chromatography (RP-HPLC) from the salivary glands of the black fly Simulium bannaense. The amino acid sequence of SibaDef was determined by a combination method of automated Edman degradation and cDNA sequencing. The morphologic changes of Gram-positive bacteria Staphylococcus aureus or Bacillus subtilis treated with SibaDef were assessed by scanning electron microscopy (SEM). Quantitative PCR (qPCR) was performed to analyze the expression of SibaDef mRNA in whole bodies of insects after oral infection with the bacteria S. aureus or B. subtilis.
  
  
  RESULTS
  Surprisingly, the phylogenetic analysis of defensin-related amino acid sequences demonstrated that SibaDef is most closely related to defensins from the human body louse Pediculus humanus corporis (Anoplura: Pediculidae), rather than to other dipteran defensins. SibaDef showed potent antimicrobial activities against Gram-positive bacteria with minimal inhibitory concentrations (MICs) ranging from 0.83 μM to 2.29 μM. SEM analysis indicated that SibaDef killed microorganisms through the disruption of cell membrane integrity. The transcript levels of SibaDef in the bacteria-immunized flies increased with the time course, reaching maximum at 36 h and then slowly decreased from that time point.
  
  
  CONCLUSIONS
  Our results indicate that SibaDef is involved in the innate humoral response of the black fly S. bannaense, and it might play a significant role in the defence against microorganisms in both sugar and blood meals.
authors: Jiangsu Key Laboratory of Infection and Immunity, Institute of Biology and Medical Sciences, Soochow University, Suzhou, Jiangsu, China. weilin1005@126.com.
authors: Lin
authors: L
authors: Wei
authors: School of Basic Medical Sciences, Kunming Medical University, Kunming, Yunnan, China. mulixian77@163.com.
authors: Lixian
authors: L
authors: Mu
authors: College of Pharmaceutical Sciences, Soochow University, Suzhou, Jiangsu, China. wyp010@163.com.
authors: Yipeng
authors: Y
authors: Wang
authors: School of Basic Medical Sciences, Kunming Medical University, Kunming, Yunnan, China. 24606341@qq.com.
authors: Hui
authors: H
authors: Bian
authors: School of Basic Medical Sciences, Kunming Medical University, Kunming, Yunnan, China. lijunall123@163.com.
authors: Jun
authors: J
authors: Li
authors: Institute of Marine biological technology, School of Life Science and Biotechnology, Dalian University of Technology, Dalian, Liaoning, China. 358711603@qq.com.
authors: Yiling
authors: Y
authors: Lu
authors: School of Basic Medical Sciences, Kunming Medical University, Kunming, Yunnan, China. kmhanyi@163.com.
authors: Yi
authors: Y
authors: Han
authors: School of Basic Medical Sciences, Kunming Medical University, Kunming, Yunnan, China. 962620924@qq.com.
authors: Tong
authors: T
authors: Liu
authors: School of Basic Medical Sciences, Kunming Medical University, Kunming, Yunnan, China. lvjing_cn@163.com.
authors: Jing
authors: J
authors: Lv
authors: School of Basic Medical Sciences, Kunming Medical University, Kunming, Yunnan, China. 4195157@qq.com.
authors: Cuiping
authors: C
authors: Feng
authors: School of Basic Medical Sciences, Kunming Medical University, Kunming, Yunnan, China. wujing_205@163.com.
authors: Jing
authors: J
authors: Wu
authors: School of Basic Medical Sciences, Kunming Medical University, Kunming, Yunnan, China. jxauyhl@aliyun.com.
authors: Hailong
authors: H
authors: Yang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D023082:Defensins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012469:Salivary Glands / Q000737:chemistry / Q000276:immunology; D016415:Sequence Alignment; D012843:Simuliidae / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000276:immunology
chemical_list: D023082:Defensins; D019476:Insect Proteins
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