Couple action of some proteases from feather keratin-degrading bacterium B.licheniformis CP-16

A keratin-degrading bacterium, Bacillus licheniformis CP-16 (B.licheniformis CP-16), isolated from feather waste, was found to produce three extracellular proteins with protease activity. Following mass spectrometry sequencing and BLAST analysis, these proteins exhibited high similarity to γ-glutamyl transpeptidase, alkaline serine protease and thioredoxin-like protein YkuU, respectively. Genes of the three proteins and Ker A from B.licheniformis were successfully cloned into pET22b and expressed in Escherichia coli (E coli), and the four recombinant enzymes were named P-Glu, P-Alk, P-Trx, and P-Ker. P-ker showed great keratinase activity (4.9 kU/mg) and casein protease activity (6.5 kU/mg), as P-Alk showed keratinase activity (1.2 kU/mg) and casein protease activity (23 kU/mg). In contrast, both P-Glu and P-Trx displayed low levels of keratinase and casein protease activities. P-Trx had disulfide bond reductase activity (3 U/mg). When mixing with P-Trx, the other three proteases, P-Glu, P-Alk, P-Ker degraded feather keratin with keratinase activity promotion of 71 %, 40 % and 71 %. Commercial proteases (trypsin and chymotrypsin) also got keratinolytic capacity after mixing with P-Trx. These findings reveal a novel synergistic mechanism between P-Trx and other proteases in the degradation of feather keratin, leading to more efficient keratin breakdown.