Divergent evolution exists in the meso-diaminopimelate dehydrogenase (meso-DAPDH) family. Taking meso-DAPDH from Corynebacterium glutamicium ATCC13032 (CgDAPDH) and Symbiobacterium thermophilum IAM14863 (StDAPDH) as examples, the two subtypes differ in terms of their amination ability toward 2-keto acids. The significant structural difference between these two subtypes is an indel loop containing 16 amino acid residues, which exists in CgDAPDH. However, the function of the indel loop has still not been reported to date. Herein, mutagenesis, including loop insertion, loop deletion, and alanine replacement, and molecular dynamics were employed to investigate the function of the loop in CgDAPDH and the evolution of meso-DAPDH. We unveiled the pivotal role of the indel loop during the catalytic cycle of CgDAPDH, especially the R180 residue. The hydrogen-bond interactions formed between R180 and E262 maintain the correct conformation of the catalytic cavity and the catalytic H152 residue. In addition, the indel loop forms a closed hydrogen-bond network with the upstream L176 and downstream H193 residues, which stabilizes the hydrogen-bond network formed by the amino acid side chains throughout the entire protein. Our results demonstrate that the indel loop is not the driving force for the divergent evolution of meso-DAPDH. However, the indel loop affects the release pathway for meso-DAP and pyruvic acid and, more significantly, the release of meso-DAP. Overall, we have identified the importance of the indel loop in CgDAPDH and have excluded its role in the divergent evolution of the meso-DAPDH family.

Wool keratin is difficult to degrade as comparing to feathers because of its tough secondary structure. In order to develop an approach for high-value utilization of wool fiber waste by keratinolytic microorganisms, which is produced from shearing, weaving, and industrial processing of wool, screening of wool-degrading bacterium with high degradation efficiency were performed in this study. To this end, Lysobacter brunescens YQ20 was identified and characterized. The optimized conditions for wool degradation were pH 9.0 and 37°C with 20% liquid volume of Erlenmeyer flask. After fermentation, 15 essential amino acids were detected when wool fiber waste was fermented. The total amino acids produced from 1% wool per hour were 13.7 mg/L. The concentration was 8.6-fold higher than that produced by the strain Stenotrophomonas maltophilia BBE11-1, which had previously been reported to have the highest wool-degrading capacity. Our study reports the first Lysobacter strain that exhibits efficient wool degradation and yields higher concentrations of amino acids than previously reported strains. Whole-genome sequencing indicated that there were 18 keratinase-like genes in the genome of YQ20, which exhibited a long evolutionary distance from those of Bacillus. Therefore, L. brunescens YQ20 may have applications in the environmentally friendly management of wool waste as fertilizer in agriculture.