Solution structure of termicin,an antimicrobial peptide from the termite Pseudacanthotermes spiniger

The solution structure of termicin from hemocytes of the termite Pseudacanthotermes spiniger was determined by proton two-dimensional nuclear magnetic resonance spectroscopy and molecular modeling techniques. Termicin is a cysteine-rich antifungal peptide also exhibiting a weak antibacterial activity. The global fold of termicin consists of an alpha-helical segment (Phe4-Gln14) and a two-stranded (Phe19-Asp25 and Gln28-Phe33) antiparallel beta-sheet forming a "cysteine stabilized alphabeta motif" (CSalphabeta) also found in antibacterial and antifungal defensins from insects and from plants. Interestingly, termicin shares more structural similarities with the antibacterial insect defensins and with MGD-1, a mussel defensin, than with the insect antifungal defensins such as drosomycin and heliomicin. These structural comparisons suggest that global fold alone does not explain the difference between antifungals and antibacterials. The antifungal properties of termicin may be related to its marked hydrophobicity and its amphipatic structure as compared to the antibacterial defensins. [SWISS-PROT accession number: Termicin (P82321); PDB accession number: 1MM0.]     

Purification of a novel arthropod defensin from the American oyster, Crassostrea virginica

An antimicrobial peptide was purified from acidified gill extract of a bivalve mollusk, the American oyster (Crassostrea virginica), by preparative acid-urea--polyacrylamide gel electrophoresis and reversed-phase high performance liquid chromatography. The 4265.0 Da peptide had 38 amino acids, including 6 cysteines. It showed strongest activity against Gram-positive bacteria (Lactococcus lactis subsp. lactis and Staphylococcus aureus; minimum effective concentrations [MECs] 2.4 and 3.0 microg/ml, respectively) but also had significant activity against Gram-negative bacteria (Escherichia coli D31 and Vibrio parahemolyticus; MECs 7.6 and 15.0 microg/ml, respectively). Comparison of the amino acid sequence with those of other known antimicrobial peptides revealed that the novel peptide had high sequence homology to arthropod defensins, including those from other bivalves, the mussels Mytilus edulis and Mytilus galloprovincialis. This is the first antimicrobial peptide to be isolated from any oyster species and we have named it American oyster defensin (AOD).     

Bacterial exposure induces and activates matrilysin in mucosal epithelial cells

Matrilysin, a matrix metalloproteinase, is expressed and secreted lumenally by intact mucosal and glandular epithelia throughout the body, suggesting that its regulation and function are shared among tissues. Because matrilysin is produced in Paneth cells of the murine small intestine, where it participates in innate host defense by activation of prodefensins, we speculated that its expression would be influenced by bacterial exposure. Indeed, acute infection (10-90 min) of human colon, bladder, and lung carcinoma cells, primary human tracheal epithelial cells, and human tracheal explants with type 1-piliated Escherichia coli mediated a marked (25-50-fold) and sustained (>24 h) induction of matrilysin production. In addition, bacterial infection resulted in activation of the zymogen form of the enzyme, which was selectively released at the apical surface. Induction of matrilysin was mediated by a soluble, non-LPS bacterial factor and correlated with the release of defensin-like bacteriocidal activity. Bacteria did not induce matrilysin in other cell types, and expression of other metalloproteinases by epithelial cells was not affected by bacteria. Matrilysin was not detected in germ-free mice, but the enzyme was induced after colonization with Bacteroides thetaiotaomicron. These findings indicate that bacterial exposure is a potent and physiologically relevant signal regulating matrilysin expression in epithelial cells.     

Stimulation of bacterial adherence by neutrophil defensins varies among bacterial species but not among host cell types

Adherence of Haemophilus influenzae to bronchial epithelial cells is enhanced by neutrophil defensins, which are released from activated neutrophils during inflammation [Gorter et al. (1998) J. Infect. Dis. 178, 1067-1078]. In this study, we showed that the adherence of H. influenzae to various epithelial, fibroblast-like and endothelial cell types was significantly enhanced by defensins (20 microg ml(-1)). Defensins stimulated also the adherence of Moraxella catarrhalis, Neisseria meningitidis and nonencapsulated Streptococcus pneumoniae to the NCI-H292 cell line. In contrast, defensins did not affect the adherence of Pseudomonas aeruginosa, encapsulated S. pneumoniae, Escherichia coli and Staphylococcus epidermidis. These results suggest that the defensin-enhanced adherence might support the adherence and possibly persistence of the selected bacterial species using the respiratory tract as port of entry.     

Genetic variants of human beta-defensin-1 and chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is due to interactions between cigarette smoke exposure and other risk factors. Genetic variations of human beta-defensin-1 (hBD-1), an endogenous antimicrobial peptide in the airway, were investigated in 60 patients and 213 healthy volunteers by single-strand conformation and restriction fragment length polymorphism analysis and DNA sequencing. Four nucleotide variations in the 5' and 3' untranslated regions and two nonsynonymous substitutions in the coding region were identified. Of these, a newly found Ile38 variant was observed in 15.0% of patients but only in 2.8% of healthy individuals and was significantly associated with the disease (OR = 6.1, 95% confidence intervals 2.0-8.3, P = 0.0012). More than 80% of those with Ile38 experienced sputum production for more than 3 months during the follow-up period. Genetic variations in hBD-1 may define a high-risk subgroup of COPD where the component of chronic bronchitis is predominant.     

通过根瘤农杆菌介导法获得菊花转基因植株

以带叶茎段为外植体,通过根癌农杆菌介导法,将兔防御素NP－1基因导入菊花品种“001”中。经梯度卡那霉素（kanamycin,Km）筛选,获得了大量Km抗性植株,其中部分Km抗性植株经Southem杂交鉴定为转基因植株。从而成功地建立了菊花遗传转化系统,为菊花分子育种奠定了基础。     

人防御素-1(HNP-1)在烟草原生质体中的瞬间表达

原生质体瞬间表达系统一般用于研究特定基因5′和3′端不同序列在相应基因表达中的作用、不同启动子对于特定基因的转录活性及为外源基因最终导入植株摸索实验条件,而将其用于研究动物基因在植物细胞中的表达情况则少见报道。     

Negative‐assortative mating for color in wolves

There is strong negative‐assortative mating for gray and black pelage color in the iconic wolves in Yellowstone National Park. This is the first documented case of significant negative‐assortative mating in mammals and one of only a very few cases in vertebrates. Of 261 matings documented from 1995 to 2015, 63.6% were between gray and black wolves and the correlation between mates for color was –0.266. There was a similar excess of matings of both gray males × black females and black males × gray females. Using the observed frequency of negative‐assortative mating in a model with both random and negative‐assortative mating, the estimated proportion of negative‐assortative mating was 0.430. The estimated frequency of black wolves in the population from 1996 to 2014 was 0.452 and these frequencies appear stable over this 19‐year period. Using the estimated level of negative‐assortative mating, the predicted equilibrium frequency of the dominant allele was 0.278, very close to the mean value of 0.253 observed. In addition, the patterns of genotype frequencies, that is, the observed proportion of black homozygotes and the observed excess of black heterozygotes, are consistent with negative‐assortative mating. Importantly these results demonstrate that negative‐assortative mating could be entirely responsible for the maintenance of this well‐known color polymorphism.