SM-1-TA and SM-2-TA: Heterologous Expression, Enzymatic/Structural Characterization, and Functional Complementarity...

Tannase is an industrial enzyme with broad application potential in areas such as the food industry. In this study, two tannase isoenzymes, SM-1-TA and SM-2-TA, were identified from Streptomyces avermitilis and comparatively analyzed for their bioinformatic and enzymatic properties. The optimal temperature for SM-1-TA and SM-2-TA was 35°C and 45°C, respectively, while their optimal pH was 7.0 and 8.0. Notably, SM-2-TA exhibited high thermal stability, retaining 40.03% residual activity after incubation at 40°C for 2 h. Most metal ions and chemical reagents inhibited the catalytic activity of both SM-1-TA and SM-2-TA. Meanwhile, compared to SM-1-TA, SM-2-TA demonstrated greater tolerance to organic reagents. When methyl gallate, propyl gallate, and tannic acid were used as substrates, the k_cat/K_m of SM-1-TA was 77.59, 63.53, and 198.31 s^{- 1} mM^{- 1}, respectively, while those of SM-2-TA were 44.65, 23.43, and 473.67 s^{- 1} mM^{- 1}, respectively. Molecular dynamics (MD) simulations suggested that the lower thermal stability of SM-1-TA may originate from its higher overall flexibility and pronounced local fluctuations within the residue region 100-150. The functional complementarity between SM‑1‑TA and SM‑2‑TA observed in this study highlights the ecological significance of isoenzymes in microbial adaptation to diverse environments. These findings not only provide insights into the functional divergence of isoenzymes but also establish a foundation for the future discovery and engineering of tannases with enhanced properties.