In vitro maturation pathway of a glutamyl endopeptidase precursor from Bacillus licheniformis

Structural insights into the role of the N-terminus in the activation and function of extracellular serine protease from Staphylococcus epidermidis

Extracellular serine protease (Esp) from Staphylococcus epidermidis is a glutamyl endopeptidase that inhibits the growth and formation of S. aureus biofilms. Previously, crystal structures of the matured and active Esp have been determined. Interestingly, many of the staphylococcal glutamyl endopeptidase zymogens, including V8 from Staphylococcus aureus and Esp from S. epidermidis, contain unusually long pro-peptide segments; however, their function is not known. With the aim of elucidating the function of these pro-peptide segments, crystal structures of the Esp zymogen (Pro-Esp) and its variants were determined. It was observed that the N-terminus of the Pro-Esp crystal structure is flexible and is not associated with the main body of the enzyme, unlike in the known active Esp structure. In addition, the loops that border the putative substrate-binding pocket of Pro-Esp are flexible and disordered; the structural components that are responsible for enzyme specificity and efficiency in serine proteases are disordered in Pro-Esp. However, the N-terminal locked Pro-Esp variants exhibit a rigid substrate-binding pocket similar to the active Esp structure and regain activity. These structural studies highlight the role of the N-terminus in stabilizing the structural components responsible for the activity and specificity of staphylococcal glutamyl endopeptidases.

Trends in extracellular serine proteases of bacteria as detergent bioadditive: alternate and environmental friendly tool for detergent industry

Proteases, one of the largest groups of industrial enzymes occupy a major share in detergent industry. To meet the existing demands, proteases with efficient catalytic properties are being explored from bacteria residing in extreme habitats. Alkaline proteases are also considered as promising candidates for industrial sectors due to the activity and stability under alkaline and harsh environment. Therefore, a systematic review on experimental studies of bacterial proteases was conducted with emphasis on purification, characterization, cloning and expression and their suitability as detergent additive. Relevant searches using a combination of filters/keywords were performed in the online databases; PubMed, Science Direct, Scopus and Web of Science. Over thousands of research papers, 71 articles in Scopus, 48 articles in Science Direct, 18 articles in PubMed and 8 articles in Web of Science were selected with regard to bacterial extracellular proteases till date. Selected articles revealed majority of the studies conducted between the years 2015 and 17 and were focused on purification of proteases from bacteria. Among microbes, a total of 41 bacterial genera have been explored with limited studies from extreme habitats. Majority of the studies have reported the involvement of subtilisin-like serine proteases with effective properties for detergent industries. The studies revealed shifting of trend from purification to cloning to genetic engineering to meet the industrial demands. The present systematic review describes the proteases from extremophilic bacteria and use of biotechnological techniques such as site-directed mutagenesis and codon optimization to engineer enzymes with better hot spots in the active sites to meet industrial challenges.

Autocatalytic activation of a thermostable glutamyl endopeptidase capable of hydrolyzing proteins at high temperatures

Glutamyl endopeptidases (GSEs) specifically hydrolyze peptide bonds formed by α-carboxyl groups of Glu and Asp residues. We cloned the gene for a thermophilic GSE (designated TS-GSE) from Thermoactinomyces sp. CDF. A proform of TS-GSE that contained a 61-amino acid N-terminal propeptide and a 218-amino acid mature domain was produced in Escherichia coli. We found that the proform possessed two processing sites and was capable of autocatalytic activation via multiple pathways. The N-terminal propeptide could be autoprocessed at the Glu^-1-Ser¹ bond to directly generate the mature enzyme. It could also be autoprocessed at the Glu^-12-Lys^-11 bond to yield an intermediate, which was then converted into the mature form after removal of the remaining part of the propeptide. The segment surrounding the two processing sites was flexible, which allowed the proform and the intermediate form to be trans-processed into the mature form by either active TS-GSE or heterogeneous proteases. Deletion analysis revealed that the N-terminal propeptide is important for the correct folding and maturation of TS-GSE. The propeptide, even its last 11-amino acid peptide segment, could inhibit the activity of its cognate mature domain. The mature TS-GSE displayed a temperature optimum of 85 °C and retained approximately 90 % of its original activity after incubation at 70 °C for 6 h, representing the most thermostable GSE reported to date. Mutational analysis suggested that the disulfide bonds Cys³²-Cys⁴⁸ and Cys¹⁸⁰-Cys¹⁸³ cumulatively contributed to the thermostability of TS-GSE.

A new strategy for recovery of two peptides without Glu employing glutamate-specific endopeptidase from Bacillus licheniformis

The difficulty in the purification of bioactive peptide limited its application in food, drug and cosmetic industry. Here we report a new strategy for the recovery of two peptides employing glutamate-specific endopeptidase from Bacillus licheniformis (GSE-BL), which shows strong specificity for Glu residue. Human glucagon and human beta-defensin-2 (HBD-2) were peptides without Glu residue, and Glu residue was introduced between affinity tag and target peptide as recognition site of GSE-BL. Tagless human glucagon with the same HPLC retention time as native human glucagon and mature HBD-2 with antibacterial activity and cytotoxicity were obtained after GSE-BL treatment. This strategy has great potential in the recovery of bioactive peptide without Glu residue, thus facilitating large scale preparation of peptide and widening the application of bioactive peptide.

Characterization of the glutamate-specific endopeptidase from Bacillus licheniformis expressed in Escherichia coli

Glutamate-specific endopeptidase from Bacillus licheniformis (GSE-BL) is widely used in peptide recovery and synthesis because of its unique substrate specificity. However, the mechanism underlying its specificity is still not thoroughly understood. In this study, the roles of the prosegment and key amino acids involved in the proteolytic activity of GSE-BL were investigated. Loss of the GSE-BL prosegment severely restricted enzymatic activity toward Z-Phe-Leu-Glu-pNA. A homologous model of GSE-BL revealed that it contains the catalytic triad "His47, Asp96 and Ser 167", which was further confirmed by site-directed mutagenesis. In vitro mutagenesis further indicated that Val2, Arg89 and His190 are essential for enzymatic activity toward Z-Phe-Leu-Glu-pNA. Moreover, the catalytic efficiency of Phe57Ala GSE-BL toward Z-Phe-Leu-Glu-pNA was 50% higher than that of the native mature GSE-BL. This is the first study to fully elucidate the key amino acids for proteolytic activity of GSE-BL. Mature GSE-BL could be obtained through self-cleavage alone when Lys at -1 position was replaced by Glu, providing a new strategy for the preparation of mature GSE-BL. This study yielded some valuable insights into the substrate specificity of glutamate-specific endopeptidase, establishing a foundation for broadening the applications of GSE-BL.

Improvement of Vitreoscilla hemoglobin function by Bacillus licheformis glutamate-specific endopeptidase treatment

Vitreoscilla hemoglobin (VHb) was widely used in metabolic engineering to improve oxygen utilization in the low oxygen environment. It is sometimes necessary to remove affinity tags because they may impede functions of target proteins. Here we report an efficient method employing Glutamate-specific endopeptidase from Bacillus licheformis (GSE-BL) to perform the cleavage between VHb and His-tag. The optimal length of GSE-BL treatment was 15min. Results of SDS-PAGE and western blot demonstrated that the His-tag of VHb-His(6) was nearly completely removed, the purity of VHb was enhanced from 74% to 99.5%, and the yield of tagless VHb from VHb-His(6) was 92.2%. Results of CO difference spectrum suggested that tagless VHb was more prone to bind to CO compared with VHb-His(6). It was observed that tagless VHb displayed higher catalase activity than VHb-His(6). The enhancement of welan gum yield was more significant by addition of tagless VHb compared with addition of VHb-His(6). This method can be utilized to mass-produce tagless VHb, thus widening the application of VHb in various industries.

Cloning, expression, purification, and characterization of a glutamate-specific endopeptidase from Bacillus licheniformis

A gene encoding a glutamate-specific endopeptidase (GSE) from Bacillus licheniformis (BL) has been cloned in Escherichia coli cells. The recombinant protein was expressed as cytoplasmic insoluble inclusion bodies. Immobilized metal affinity chromatography was employed to purify the protein, and then a 27-kDa GSE intermediate was obtained by gradient urea dialysis. The remaining pro-peptide was completely removed by treatment with trypsin to obtain mature GSE-BL with a molecular weight of 26 kD at a final yield of up to 140.9 mg/L. With Z (benzyloxycarbomyl)-Phe-Leu-Glu-pNA (p-nitroanilide) as the substrate, the optimal temperature and pH conditions for the enzyme were 37 °C and 8.5, respectively, K(m) was 1.495 ± 0.034 mM, and V(max) was 50.237 μmol/mg min. The presence of calcium and ferrous ions enhanced the catalytic activity of GSE-BL. These results suggest that the recombinant protein is a relatively stable specific proteinase that could be effectively utilized in protein structure analysis, peptide synthesis, and the food industry.

[Effect of a modification of the processing site of Bacillus intermedius glutamyl endopeptidase on the production of active enzyme by Bacillus subtilis cells]

A site-directed modification in position P1 of the processing site of Bacillus intermedius glutamyl endopeptidase was carried out. Variants of the protease gene were obtained that correspond to the protein with an Ala, Asn, Ser, or Glu residue in this position substituted for the Lys residue. The residue in the P1 position of the processing site was shown to affect substantially the production of the active enzyme; however, none of the mutations leads to the complete termination of active protein production by cells.