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Indole and its derivatives are valuable compounds used in flavor, fragrance, and pharmaceutical industries. Tryptophanase (TnaA, EC 4.1.99.1) catalyzes the conversion of L-tryptophan into indole, pyruvate, and ammonia, but limited thermostability restricts its industrial application. Here, a thermostable TnaA from Morganella morganii was identified through ancestral sequence analysis, structural prediction, and molecular dynamics simulations. The enzyme existed mainly as a dimer under native conditions and showed optimal activity at 55 °C and pH 8.0. Compared with the commonly used Proteus vulgaris TnaA, M. morganii TnaA exhibited an 8.8 °C higher Tm, a 9.1 °C higher T5030, and an 18-fold longer half-life at 45 °C. Substrate specificity analysis showed activity only toward L-tryptophan and l-serine. These properties make M. morganii TnaA a promising biocatalyst for thermostable indole production.
Zhang et al. (Mon,) studied this question.