Efficient Hydrolysis of Gluten-Derived Celiac Disease-Triggering Immunogenic Peptides by a Bacterial Serine Protease from Burkholderia gladioli

Specificity Enhancement of Glutenase Bga1903 toward Celiac Disease-Eliciting Pro-Immunogenic Peptides via Active-Site Modification

Celiac disease is an autoimmune disease triggered by oral ingestion of gluten, with certain gluten residues resistant to digestive tract enzymes. Within the duodenum, the remaining peptides incite immunogenic responses, including the generation of autoantibodies and inflammation, leading to irreversible damage. Our previous exploration unveiled a glutenase called Bga1903 derived from the Gram-negative bacterium Burkholderia gladioli. The cleavage pattern of Bga1903 indicates its moderate ability to mitigate the toxicity of pro-immunogenic peptides. The crystal structure of Bga1903, along with the identification of subsites within its active site, was determined. To improve its substrate specificity toward prevalent motifs like QPQ within gluten peptides, the active site of Bga1903 underwent site-directed mutagenesis according to structural insights and enzymatic kinetics. Among the double-site mutants, E380Q/S387L exhibits an approximately 34-fold increase in its specificity constant toward the QPQ sequence, favoring glutamines at the P1 and P3 positions compared to the wild type. The increased specificity of E380Q/S387L not only enhances its ability to break down pro-immunogenic peptides but also positions this enzyme variant as a promising candidate for oral therapy for celiac disease.

Hydrolysis of Gluten-Derived Celiac Disease-Triggering Peptides across a Broad pH Range by RmuAP1: A Novel Aspartic Peptidase Isolated from Rhodotorula mucilaginosa

An aspartate peptidase with proteolytic activity toward gluten was identified from an isolated red yeast Rhodotorula mucilaginosa strain. This peptidase consists of 425 amino acids, comprising an N-terminal signal peptide, a propeptide, and a C-terminal catalytic domain. The catalytic domain, termed RmuAP1CD, could be secreted by the recombinant oleaginous yeast Yarrowia lipolytica, whose genome contains the expression cassette for RmuAP1CD. RmuAP1CD exhibited optimum activity at pH 2.5 when acting on bovine serum albumin. Moreover, it facilitated the hydrolysis of gluten-derived immunogenic peptides (GIPs), which are responsible for triggering celiac disease symptoms, across a pH range of 3.0-6.0. The preferred cleavage sites are P-Q-Q-↓-P-Q in the 26-mer and P-Q-L-↓-P-Y in the 33-mer GIPs. Conversely, porcine pepsin cannot hydrolyze these two GIPs. The ability of RmuAP1CD to degrade GIPs under acidic conditions of the stomach indicates its potential as a viable oral enzyme therapy for celiac disease.

Gut microbiota predicts the diagnosis of celiac disease in Saudi children

BACKGROUND

Celiac disease (CeD) is a multisystem immune-mediated multifactorial condition strongly associated with the intestinal microbiota.

AIM

To evaluate the predictive power of the gut microbiota in the diagnosis of CeD and to search for important taxa that may help to distinguish CeD patients from controls.

METHODS

Microbial DNA from bacteria, viruses, and fungi, was isolated from mucosal and fecal samples of 40 children with CeD and 39 controls. All samples were sequenced using the HiSeq platform, the data were analyzed, and abundance and diversities were assessed. For this analysis, the predictive power of the microbiota was evaluated by calculating the area under the curve (AUC) using data for the entire microbiome. The Kruskal-Wallis test was used to evaluate the significance of the difference between AUCs. The Boruta logarithm, a wrapper built around the random forest classification algorithm, was used to identify important bacterial biomarkers for CeD.

RESULTS

In fecal samples, AUCs for bacterial, viral, and fungal microbiota were 52%, 58%, and 67.7% respectively, suggesting weak performance in predicting CeD. However, the combination of fecal bacteria and viruses showed a higher AUC of 81.8 %, indicating stronger predictive power in the diagnosis of CeD. In mucosal samples, AUCs for bacterial, viral, and fungal microbiota were 81.2%, 58.6%, and 35%, respectively, indicating that mucosal bacteria alone had the highest predictive power. Two bacteria, Bacteroides intestinalis and Burkholderiales bacterium 1-1-47, in fecal samples and one virus, Human_endogenous _retrovirus_K, in mucosal samples are predicted to be “important” biomarkers, differentiating celiac from nonceliac disease groups. Bacteroides intestinalis is known to degrade complex arabinoxylans and xylan which have a protective role in the intestinal mucosa. Similarly, several Burkholderiales species have been reported to produce peptidases that hydrolyze gluten peptides, with the potential to reduce the gluten content of food. Finally, a role for Human_endogenous _retrovirus_K in immune-mediated disease such as CeD has been reported.

CONCLUSION

The excellent predictive power of the combination of the fecal bacterial and viral microbiota with mucosal bacteria alone indicates a potential role in the diagnosis of difficult cases of CeD. Bacteroides intestinalis and Burkholderiales bacterium 1-1-47, which were found to be deficient in CeD, have a potential protective role in the development of prophylactic modalities. Further studies on the role of the microbiota in general and Human_endogenous _retrovirus_K in particular are needed.

Human small-intestinal gluten-degrading bacteria and its potential implication in celiac disease

Celiac disease (CeD) is an immune-mediated chronic disorder triggered by the ingestion of wheat gluten in genetically predisposed individuals. Gluten is a major food ingredient, infamously containing proline and glutamine-rich domains that are highly resistant to digestion by mammalian proteolytic enzymes. Thus, adhering to a gluten-free diet (GFD) is the only known treatment for CeD, albeit with many complications. Therefore, any therapy that eliminates the gluten immunogenic part before it reaches the small intestine is highly desirable. Probiotic therapy containing gluten-degrading bacteria (GDB) and their protease enzymes are possibly new approaches to treating CeD. Our study aimed to identify novel GDB from the duodenal biopsy of the first-degree relative (FDR) subjects (relatives of diseased individuals who are healthy but susceptible to celiac disease) with the potential to reduce gluten immunogenicity. Using the gluten agar plate technique, bacterial strains Brevibacterium casei NAB46 and Staphylococcus arlettae R2AA77 displaying glutenase activity were screened, identified, and characterized. Whole-genome sequencing found gluten-degrading prolyl endopeptidase (PEP) in the B. casei NAB46 genome and glutamyl endopeptidase (GEP) in the S. arlettae R2AA77 genome. Partially purified PEP has a specific activity of 1.15 U/mg, while GEP has a specific activity of 0.84 U/mg, which are, respectively, 6- and 9-fold times higher after concentrating the enzymes. Our results showed that these enzymes could hydrolyse immunotoxic gliadin peptides recognized in western blot using an anti-gliadin antibody. Additionally, a docking model was proposed for representative gliadin peptide PQPQLPYPQPQLP in the active site of the enzymes, where the residues of the N-terminal peptide extensively interact with the catalytic domain of the enzymes. These bacteria and their associated glutenase enzymes efficiently neutralize gliadin immunogenic epitopes, opening possibilities for their application as a dietary supplement in treating CeD patients.

Characterization of Bacillus cereus AFA01 Capable of Degrading Gluten and Celiac-Immunotoxic Peptides

Wheat gluten elicits a pro-inflammatory immune response in patients with celiac disease. The only effective therapy for this disease is a life-long gluten-free diet. Gluten detoxification using glutenases is an alternative approach. A key step is to identify useful glutenases or glutenase-producing organisms. This study investigated the gluten-degrading activity of three Bacillus cereus strains using gluten, gliadin, and highly immunotoxic 33- and 13-mer gliadin peptides. The strain AFA01 was grown on four culture media for obtaining the optimum gluten degradation. Complete genome sequencing was performed to predict genes of enzymes with potential glutenase activity. The results showed that the three B. cereus strains can hydrolyze gluten, immunotoxic peptides, and gliadin even at pH 2.0. AFA01 was the most effective strain in degrading the 33-mer peptide into fractions containing less than nine amino acid residues, the minimum peptide to induce celiac responses. Moreover, growth on starch casein broth promoted AFA01 to degrade immunotoxic peptides. PepP, PepX, and PepI may be responsible for the hydrolysis of immunotoxic peptides. On the basis of the potential of gluten degradation, AFA01 or its derived enzymes may be the best option for further research regarding the elimination of gluten toxicity.