[Enhancing thermostability of xylanase from rumen microbiota by molecular cyclization]

The capacity for thermal tolerance is critical for industrial enzyme. In the past decade, great efforts have been made to endow wild-type enzymes with higher catalytic activity or thermostability using gene engineering and protein engineering strategies. In this study, a recently developed SpyTag/SpyCatcher system, mediated by isopeptide bond-ligation, was used to modify a rumen microbiota-derived xylanase XYN11-6 as cyclized and stable enzyme C-XYN11-6. After incubation at 60, 70 or 80 ℃ for 10 min, the residual activities of C-XYN11-6 were 81.53%, 73.98% or 64.41%, which were 1.48, 2.92 or 3.98-fold of linear enzyme L-XYN11-6, respectively. After exposure to 60-90°C for 10 min, the C-XYN11-6 remained as soluble in suspension, while L-XYN11-6 showed severely aggregation. Intrinsic and 8-anilino-1-naphthalenesulfonic acid (ANS)-binding fluorescence analysis revealed that C-XYN11-6 was more capable of maintaining its conformation during heat challenge, compared with L-XYN11-6. Interestingly, molecular cyclization also conferred C-XYN11-6 with improved resilience to 0.1-50 mmol/L Ca²⁺ or 0.1 mmol/L Cu²⁺ treatment. In summary, we generated a thermal- and ion-stable cyclized enzyme using SpyTag/SpyCatcher system, which will be of particular interest in engineering of enzymes for industrial application.