title: Alkaline protease inhibitor: a novel class of antifungal proteins against phytopathogenic fungi.
abstract: 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.
authors.affiliation: Division of Biochemical Sciences, National Chemical Laboratory, Pune, 411008, India.
authors.forename: J V
authors.initials: JV
authors.lastname: Vernekar
authors.forename: M S
authors.initials: MS
authors.lastname: Ghatge
authors.forename: V V
authors.initials: VV
authors.lastname: Deshpande
mesh_terms: D000528:Alternaria / Q000187:drug effects; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D000935:Antifungal Agents / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D019281:Dimerization; D005658:Fungi / Q000187:drug effects* / Q000201:enzymology; D005670:Fusarium / Q000187:drug effects; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D008855:Microscopy, Electron, Scanning; D010455:Peptides; D011480:Protease Inhibitors / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D012232:Rhizoctonia / Q000187:drug effects; D012697:Serine Endopeptidases / Q000302:isolation & purification / Q000378:metabolism*; D012988:Soil Microbiology; D013302:Streptomyces / Q000145:classification / Q000502:physiology* / Q000648:ultrastructure; D014242:Trichoderma / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D000935:Antifungal Agents; D010455:Peptides; D011480:Protease Inhibitors; C038356:microbial alkaline proteinase inhibitor; D012697:Serine Endopeptidases