Proposed mechanism for post‐translational self‐modification of Co‐NHase based on Co²⁺ diffusion limitation

Abstract

Background: Nitrile hydratase (NHase), was an excellent biocatalyst for the synthesis of amide compounds. NHase was typical heterodimeric metalloprotein, required of the assistance of activator for active expressions. In this work, we found a special Co-NHase HBA from Caldalkalibacillus thermarum, which had the ability of posttranslational self-modification and could incorporate Co 2+ into the catalytic center in the absence of activator. Method and Results:We simulated the movement of Co 2+ in silico and established a hypothetical model to predict the Co 2+ incorporation efficiency (X Co ) of NHases.According to the simulation results, NHase mutants with different positive charge distribution were constructed. Compared with wild-type, the Co 2+ incorporation efficiency of K1 (M10K) was increased by 2.1-fold from 0.36 to 0.76, and the specific activity was increased by 3.2-fold from 136.3 to 432.0 U mg -1 , while mutant K1H1 (M10K, D11H) and K2H2 (M10K, D11H, E20K, N21H) lost the ability of post-translation selfmodification. Conclusions and Implications:The interactions of positively charged residues near the catalytic center, such as lysine with strong electrostatic repulsive interaction, arginine with weak electrostatic repulsive interaction and histidine with metal affinity, could limit the free diffusion of Co 2+ in NHase and affect the efficiency of post-translational self-modification. This work also provided an effective strategy for protein engineering of NHases and other metalloenzymes.

High‐Throughput Screening of Signal Peptide Library with Novel Fluorescent Probe

“…NHase was a special metalloenzyme, which was composed of two heterologous subunits and the activator was required to participate in the post-translational modification to complete the active expression. The NHase HBA with the ability of posttranslational self-modification and high specific activity after subunit-fusion expression was obtained in our previous research, [23] which made the secretory expression of NHase possible. In addition, B. subtilis was one of the host cells commonly used for heterologous expression of secreted proteins.…”