Abstract
Background
The AA9 (auxiliary activities) family of lytic polysaccharide monooxygenases (AA9 LPMOs) are ubiquitous and diverse group of enzymes amongst the fungal kingdom. They catalyze the oxidative cleavage of glycosidic bonds in lignocellulose and exhibit great potential for secondary biorefinery applications. Screening of AA9 LPMOs for desirable properties is crucial for biorefinery industrial applications. However, robust, high-throughput and direct method for AA9 LPMO activity assay, which is prerequisite for screening of LPMOs with excellent properties, is still lacking. Here, we have described a gluco-oligosaccharide oxidase (GOOX) based horseradish peroxidase (HRP) colorimetric method for AA9 LPMO activity assay.
Results
We cloned and expressed a GOOX gene from Sarocladium strictum in Trichoderma reesei, purified the recombinant SsGOOX, validated its properties, and set up a SsGOOX based HRP colorimetric method for cellobiose concentration assay. Then we expressed two AA9 LPMOs from Thielavia terrestris, TtAA9F and TtAA9G in T. reesei, purified the recombinant proteins, and analyzed their product profiles and regioselectivity towards phosphoric acid swollen cellulose (PASC). TtAA9F was characterized as a C1 type (class 1) LPMO, while TtAA9G was characterized as a C4 type (class 2) LPMO. Finally, the SsGOOX based HRP colorimetric method was used to quantify the total concentration of reducing lytic products from LPMO reaction, and consequently, the activities of both C1 and C4 types of LPMOs were analyzed. These LPMOs could be effectively analyzed with limits of detection (LoDs) lower than 30 nmol/L, and standard curves between A515 and LPMO concentrations with determination coefficients greater than 0.994 were obtained.
Conclusions
A novel, sensitive and accurate assay method that directly targets the main activity of both C1 and C4 type of AA9 LPMOs was established. This method is easy to use and could be performed on a microtiter plate ready for high-throughput screening of AA9 LPMOs with high properties.
A sensitive, accurate, and high-throughput gluco-oligosaccharide oxidase based HRP colorimetric method for lytic polysaccharide monooxygenase activity assay