# Molecular Identification of Keratinase DogkerA from Deinococcus gobiensis for Feather Degradation
## 1 Introduction  
Keratin is rich in nutrients and contains up to 70% of various amino acids, such as cysteine, lysine, proline and serine, which makes it a potentially valuable protein [1]. Keratin is difficult to degrade and utilize due to the strong properties conferred by the huge cross-linking of disulfide and hydrogen bonds, and the recycling of keratin of animal origin, which is produced by the poultry industry at over 1 billion tons per year, has become a challenge for the industry [2, 3]. Keratinase acts specifically on the disulfide bonds of keratin and, thus, hydrolyses keratin [4]. Keratinases are widely found in microorganisms and the use of keratinases to recover keratin-related resources is an environmentally friendly, low energy consuming and sustainable approach [5]. Keratin hydrolyses or keratinases (EC 3.4.21/24/99.11) are classified as serine proteases, aspartate proteases, metalloproteinases and serine-metal complex proteases, depending on the inhibition of the amino acid group in the active site of the protease [4]. Among them, the serine keratinase group is the most numerous and widely used, represented by _Bacillus_ keratinases. _Bacillus licheniformis_ PWD-1 is able to grow and ferment in feather digesters in both anaerobic and aerobic environments [6]. BliKerA, derived from _B. licheniformis_ PWD-1 keratinase, is the most well-studied keratinase. BlikerA has been successfully expressed in different hosts, such as _Bacillus subtilis_, _Bacillus megaterium_, andPichia pastoris_, it has been developed into the commercial enzyme \"Versazyme\" and is widely used as a nutrient preparation. The keratinase sequence contains a signal peptide, an N-terminal propeptide and a mature region, and some keratinases contain C-terminal extensions [7]. _B. licheniformis_ PWD-1 keratinase BliKerA contains only the signal peptide, the N-terminal prepeptide and the mature region, whereas _Thermococcus kodakanensis_ keratinase ProN-Tk-SP contains these three structures in addition to the C-terminal extension structure [6,8]. The signal peptide directs the secretion of the keratinase to its extracellular function, while the N-terminal propeptide usually acts as an intramolecular chaperone to facilitate the correct folding of the keratinase structure [9]. The major structures of the keratinase mature region are the catalytic active center and the substrate recognition site. The activity center contains the Asp-His-Ser catalytic triad. The gap adjacent to the three catalytic residues becomes the S1 pocket, and the spatial structure and hydrophobicity of the S1 pocket affects the catalytic activity of keratinases [10,11]. In addition, the enzymes generally contain calcium-binding sites, which contribute to the thermal stability of keratinases [3,12]. Extremophiles are considered a valuable source for the production of novel enzymes due to their unique metabolism and ability to withstand extreme environments, such as high temperature, high pressure, high pH and high radiation [13, 14, 15]. Many studies have been conducted to identify keratinases with excellent properties from extremophiles, such as _Nocardiopsis_[16], _Salicola Marasensis_[17] and _Meiothermus taiwanensis_ WR-220 [7]. _M. taiwanensis_ WR-220 was a thermophilic microorganism with a growth temperature of 55-65 \({}^{\circ}\)C. The keratinase from this bacterium also exhibited thermal stability, maintaining intact enzymatic activity after 1 h of treatment at 75 \({}^{\circ}\)C [7]. It was shown that keratinase genes are present in extreme microorganisms _Deinococcus_[14], such as _D. geothermalis_[18] and _Deinococcus_ sp. D7/000 [19], and that the feather-degrading bacteria _D. ficus_[20] and _D. radiodurans_ R1 [14] are able at 30 \({}^{\circ}\)C to degrade intact feathers. In this study, the keratinase DgoKerA was identified from the Gobi-derived _D. gobiensis_ I-0 by comparative genomic analysis. Structurally, DgoKerA possessed a signal peptide, an N-terminal propeptide and a mature region, as did the classical keratinase BliKerA.