A Streptomyces sp., which produces an alkaline protease inhibitor (API) exhibiting antifungal activity has been isolated from soil. The protein has been purified to homogeneity. The molecular characterization has reve...
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A Streptomyces sp., which produces an alkaline protease inhibitor (API) exhibiting antifungal activity has been isolated from soil. The protein has been purified to homogeneity. The molecular characterization has revealed that it is a dimer (M-r 28 kDa) with five disulphide linkages and has a pI of 3.8. API is a competitive type of inhibitor with a K-i value of 2.5 x 10(-9) M. The inhibitor is stable over a pH range of 6 to 12 and a temperature range of 40 to 95 degrees C. API exhibits antifungal activity (in vitro) against phytopathogenic fungi such as Fusarium, Alternaria, and Rhizoctonia and also against Trichoderma, a saprophytic fungus. The antifungal activity of API appears to be associated with its ability to inhibit the fungal serine alkaline protease(s), which is indispensable for its growth. Retardation of the rate of fungal spore germination, as well as hyphal extention, was observed in the presence of API. Both the protease inhibitory and the antifungal activity were abolished on treatment of API with DTT (5 mM), suggestive of a common site for both the activities. This is the first report on API as a potential biocontrol agent against phytopathogenic fungi. (C) 1999 Academic Press.
Four macrocyclic cystine-knot peptides of 29-31 residues, kalata, circulin A and B (CirA and CirB), and cyclopsychotride, have been isolated from coffee plants but have undetermined physiological functions. These macr...
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Four macrocyclic cystine-knot peptides of 29-31 residues, kalata, circulin A and B (CirA and CirB), and cyclopsychotride, have been isolated from coffee plants but have undetermined physiological functions. These macrocycles and 10 of their analogs prepared by chemical synthesis were tested against nine strains of microbes. Kalata and CirA were specific for the Gram-positive Staphylococcus aureus with a minimum inhibition concentration of approximate to 0.2 mu M. They were relatively ineffective against Gram-negative bacteria such as Escherichia coli and Pseudomonas aeruginosa. However, CirB and cyclopsychotride mere active against both Gram-positive and Gram-negative bacteria. In particular, CirB showed potent activity against E. coli with a minimum inhibitory concentration of 0.41 mu M. All four cyclic peptides were moderately active against two strains of fungi, Candida kefyr and Candida tropicalis, but were inactive against Candida albicans, These macrocycles are cytotoxic and lysed human red blood cell with a lethal dose 50% of 400 mu M. Modifying the Arg residue in kalata with a keto aldehyde significantly reduced its activity against S. aureus whereas blocking the arg in CirA produced no significant effect. The two-disulfide variants and their scrambled disulfide isomers exhibited antimicrobial profiles and potency similar to their native peptides, However, in high-salt assays (100 mM NaCl), few of these macrocyclic peptides, natives or analogs, retained antimicrobial activity, These results show that the macrocyclic peptides possess specific and potent antimicrobial activity that is salt-dependent and that their initial interactions with the microbial surfaces may be electrostatic, an effect commonly found in defensin antimicrobial peptides, Furthermore, their end-to-end cyclic structure with a cystine-knot motif represents a molecular structure of antimicrobials and may provide a useful template for the design of novel peptide antibiotics.
Colonization of the human stomach by the bacterium Helicobacter pylori is a predisposing factor for gastrointestinal illnesses such as gastritis and peptic ulcers. But most infections are asymptomatic, and it has rece...
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Colonization of the human stomach by the bacterium Helicobacter pylori is a predisposing factor for gastrointestinal illnesses such as gastritis and peptic ulcers. But most infections are asymptomatic, and it has recently been suggested that H. pylori may actually have beneficial effects on infected carriers who are heavily exposed to other gastrointestinal pathogens. We find that H. pylori possesses antibacterial activity to which it is itself resistant. We have traced this activity to cecropin-like amino-terminal peptides derived from the ribosomal protein L1 (RpL1).
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