Isolation and characterization of mimosine degrading enzyme from Arthrobacter sp. Ryudai-S1

Leucaena leucocephala growing in the tropics and subtropics serves as potential forage for livestock because its foliage is rich in protein, fiber, and minerals. However, its use for livestock feed has been hindered by toxic nonprotein amino acid mimosine. Therefore, it is necessary to develop a method to reduce or eliminate mimosine from foliage. A previous study found that the fermentation of L. leucocephala foliage reduced the mimosine content and prompted the authors to isolate potent mimosine degrading microorganisms and characterize the mimosinase for the complete elimination of mimosine in the L. leucocephala foliage. The soil screening of the L. leucocephala tree surroundings led to the isolation of Arthrobacter sp. Ryudai-S1, which can degrade and assimilate mimosine as a nitrogen and carbon source. Mimosinase in this strain was found to be thermostable and showed strong activity. Docking model's inspection and the interaction energy calculation between mimosine-pyridoxal-5 '-phosphate (PLP) complex and the active site of this enzyme identified 11 important amino acid residues that stabilized the binding. Of these amino acid residues, mutation experiment suggested that Tyr-263 ' and Phe-34 stabilizes the substrate binding and play a critical role in guiding the substrate to proper positions to accomplish high catalytic efficacy and selectivity. These observations suggest that Arthrobacter sp. Ryudai-S1 could be potentially useful for the development of L. leucocephala feed with reduced mimosine content.

Automated summary

Leucaena leucocephala is a potential forage for livestock due to its rich protein, fiber, and minerals. However, the presence of toxic nonprotein amino acid mimosine hinders its use as livestock feed. In this study, a microorganism called Arthrobacter sp. Ryudai-S1 was isolated from the soil surrounding L. leucocephala trees, which can degrade and assimilate mimosine as a nitrogen and carbon source. The mimosinase in this strain was found to be thermostable and showed strong activity. Further analysis identified key amino acid residues that play a critical role in substrate binding and catalytic efficacy. These findings suggest that Arthrobacter sp. Ryudai-S1 could be potentially useful for developing L. leucocephala feed with reduced mimosine content.