Properties of Two Novel Esterases Identified from Culture Supernatant of Penicillium purpurogenum Grown on Sugar Beet Pulp

BACKGROUND: The filamentous fungus Penicillium purpurogenum grows on a variety of natural carbon sources, such as sugar beet pulp, and secretes to the medium a large number of enzymes that degrade the carbohydrate components of lignocellulose. Sugar beet pulp is rich in pectin, and the purpose of this work is to identify novel esterases produced by the fungus, which may participate in pectin degradation. METHODS AND FINDINGS: Partially purified culture supernatants of the fungus grown on sugar beet pulp were subjected to mass spectrometry analysis. Peptides thus identified, which may be part of potential esterases were probed against the proteins deduced from the fungal genome sequence. The cDNAs of two putative esterases identified were expressed in Pichia pastoris and their properties studied. One of these enzymes, named FAET, is a feruloyl esterase, while the other, PE, is classified as a pectin methyl esterase. CONCLUSIONS: These findings add to our knowledge of the enzymology of pectin degradation by Penicillium purpurogenum, and define properties of two novel esterases acting on de-esterification of pectin. Their availability may be useful as tools for the study of pectin structure and degradation.