Ionic-microenvironment stabilizes the disulfide engineered lysine decarboxylase for efficient cadaverine production

Cadaverine is the key monomer for the synthesis of nylon 5X. Efficient and alkaline stable lysine decarboxylases are highly desirable for cadaverine production as the reaction pH increasing from 6.3 to 8.5. However, the most studied lysine decarboxylase CadA (E. coli) lost almost all activity at pH 8.0, which is the foremost challenge for the industrial-cadaverine production. In this study, we first found that the Na⁺-microenvironment significantly improved the alkaline stability of the disulfide engineered lysine decarboxylase ΔLdcEt3 (P233C/L628C) (half-life 362 h), compared to the conventional buffer (half-life 0.66 h) at pH 8.0. Meanwhile, the whole-cell conversion efficiency of the industrial-grade l-lysine with ΔLdcEt3 could reach up to 99% in 2 h in the fermenter. Experimental investigation and molecular dynamics confirmed that Na⁺-microenvironment could improve active-aggregation state and affect secondary structure of ΔLdcEt3. Therefore, Na⁺-microenvironment stabilizes ΔLdcEt3 providing a great potential industrial application for high-level cadaverine production.