Antifungal activity of rye (Secale cereale) seed chitinases: the different binding manner of class I and class II chitinases to the fungal cell walls.
The antifungal activities of rye seed chitinase-a (RSC-a, class I) and -c (RSC-c, class II) were studied in detail using two different bioassays with Trichoderma sp. as well as binding and degradation experiments with the cell walls prepared from its mycelia. RSC-a inhibited more strongly the re-extension of the hyphae, containing mainly mature cells, than RSC-c did. Upon incubation of the fungus with fluorescent chitinases, FITC-labeled RSC-a was found to be located in the hyphal tips, lateral walls, and septa, while FITC-labeled RSC-c was only in the hyphal tip. RSC-a had a greater affinity for the cell walls than RSC-c. RSC-a liberated a larger amount of reducing sugar from the cell walls than RSC-c did. These results inferred that RSC-a first binds to the lateral walls and septa, consisting of the mature cell walls, and degrades mature chitin fiber, while RSC-c binds only to the hyphal tip followed by degradation of only nascent chitin. As a result, RSC-a inhibited fungal growth more effectively than RSC-c. Furthermore, it was suggested that the chitin-binding domain in RSC-a assists the antifungal action of RSC-a by binding to the fungal hypha.
Taira
Toki
T
Department of Bioscience and Biotechnology, Faculty of Agriculture, Ryukyu University, Okinawa, Japan. tokey@agr.u-ryukyu.ac.jp
Ohnuma
Takayuki
T
Yamagami
Takeshi
T
Aso
Yoichi
Y
Ishiguro
Masatsune
M
Ishihara
Masanobu
M
D000935:Antifungal Agents / Q000378:metabolism / Q000494:pharmacology*; D001665:Binding Sites; D002688:Chitinases / Q000378:metabolism / Q000494:pharmacology*; D002853:Chromatography, Liquid; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D011485:Protein Binding; D012434:Secale / Q000196:embryology / Q000201:enzymology*; D012639:Seeds / Q000201:enzymology*; D014242:Trichoderma / Q000187:drug effects* / Q000378:metabolism
D000935:Antifungal Agents; D002688:Chitinases