Insights into enzyme secretion by filamentous fungi: comparative proteome analysis of Trichoderma reesei grown on...

Trichoderma reesei is the main industrial producer of lignocellulolytic enzymes, and the secretory behavior of this fungus strongly depends on the carbon sources. To gain insights into how the T. reesei adapts to various carbons and regulates enzyme production, the extra- and intracellular proteomes of T. reesei grown in defined medium with lactose or xylose as the carbon source were investigated. Results indicated that the composition of extracellular proteome differed considerably depending on the carbons. The main cellobiohydrolases, i.e. Cel7a/Cel6 were the most abundant cellulolytic enzymes identified in both media, and found to be more abundant in lactose-grown culture. As compared to lactose, xylose can serve as a potent inducer of xylanolytic enzymes. Interestingly, most identified intracellular proteins are involved in carbon metabolism. Enzymes involved in utilization of xylose, such as d-xylose reductase (Xyl1p) and d-xylose dehydrogenase (Xyl2p), were present at elevated levels in the culture growing on xylose but only in minor amounts in the lactose culture. However, lactose induction significantly activated the expression of key enzymes involved in glycolysis pathway and citrate cycle. Importantly, the protein Xyl1p which participates both in the lactose and the xylose catabolism was verified as a potential regulator for cellulase formation in T. reesei.

This study not only gives an overview of the ubiquitous cellular changes induced by the two conventional carbon substrates, but offers the framework for understanding the mechanisms behind the carbon-dependent induction of extracellular enzymes in T. reesei. Moreover, this study provides a potential target (Xyl1p) that could be tentatively used for metabolic engineering of T. reesei for cost-effective cellulase production.