Fusarium proliferatum PSA-3 Produces Xylanase-Aggregate to Degrade Complex Arabinoxylan

Xylanolytic enzymes of Fusarium species are closely associated with pathogenesis, where they soften plant cell walls to facilitate infection and nutrient uptake. This study investigated the xylanolytic system of Fusarium proliferatum PSA-3, a strain isolated from mango leaves showing dark spot symptoms. When cultivated on rice straw under solid-state fermentation, PSA-3 produced high xylanase activity against rye arabinoxylan (50.2 U) and beechwood xylan (56.8 U). Partial purification by ion-exchange and gel-filtration chromatography yielded a large xylanase aggregate (158 kDa), which appeared as a smear at the top of the gel under native conditions. Mild denaturation resolved the aggregate into at least four active proteins of ~20, 35, 48, and 63 kDa, indicating that multiple xylanases assemble into a functional aggregate. The aggregate retained activity across pH 4.0–8.0, with an optimum at pH 5.0 and 50 °C, and was resistant to Ni²⁺, Fe²⁺, Co²⁺, and β-mercaptoethanol, but inhibited by SDS. Hydrolysis of xylo-oligosaccharides (DP 2–6), purified xylans, and plant-derived xylans confirmed predominantly endo-type action with debranching activity toward A2XX and A2,3XX. These findings reveal a natural xylanase aggregate in F. proliferatum, providing a potential mechanism for efficient degradation of arabinoxylan-rich cell walls and offering targets for antifungal strategies and biotechnological applications.