Characterization of Pectinases from Brown-rot Fungus Fomitopsis palustris

IRG/WP 19-10951

Y Tanaka, N Konno, T Suzuki, N Habu

Brown-rot fungi occur on softwood used as building materials and cause destructive breakdown of wood structure. Therefore, a more accurate understanding is important from the perspective of wood protection. Previous studies have reported that hyphae of brown-rot fungi go through bordered pits on tracheids when the fungi grow into softwood [Francis W.M.R.Schwarze (2007)], and torus existing in the middle of the bordered pits contains pectin abundantly [D. Maschek et al. (2013)]. However, there is a little information on pectin degrading enzymes from brown-rot fungi. In this study, pectinases from brown-rot fungus Fomitopsis palustris were purified and characterized. Fomitopsis palustris was cultivated on the liquid medium containing 2% pectin, and the culture supernatant after the cultivation was recovered by filtration. Proteins in the supernatant were concentrated with 70% saturated (NH4)2SO4, and a polygalacturonase was purified as one of the pectinases by applying to 4 steps of column chromatography. Enzymatic activity was assayed by using sodium polygalacturonate, the main chain of pectin. Purified polygalacturonase was designated as PG-A, and its properties were analysed. Purified PG-A degraded sodium polygalacturonate acting in an endo-like manner. PG-A was not able to degrade calcium polygalacturonate gel that was prepared by mixing sodium polygalacturonate with calcium chloride in distilled water. Pectin in wood is known to be gelling with calcium ions, therefore, PG-A was suggested to degrade pectin in wood in cooperation with other molecules. We presumed that oxalic acid plays an additional role when PG-A degrades pectin in wood. PG-A was found to be able to degrade calcium polygalacturonate gel in the presence of oxalic acid. Moreover, the thermal stability of PG-A was increased in oxalate buffer at pH 3.0 compared to that in phosphate buffer at pH 7.0, which also indicates the importance of oxalate in pectin degradation by PG-A. In addition to calcium polygalacturonate gel, PG-A was unable to degrade methylesterified pectin, which has a similar structure to pectin in wood. We have partially purified pectinmethylesterase from Fomitopsis palustris, and the investigation of the relationship between PG-A and pectinmethylesterase is now under way.


Keywords: brown-rot fungi, Fomitopsis palustris, pectin, polygalacturonase

Conference: 19-05-12/16 Quebec City, Canada


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