Project description:Proteases constitute the largest enzyme gene family in vertebrates with intracellular and secreted proteases having critical roles in cellular and organ physiology. Intestinal tract contains diverse set of proteases mediating digestion, microbial responses, epithelial and immune signaling. Transit of chyme through the intestinal tract results in significant suppression of proteases. Although endogenous protease inhibitors have been identified, the broader mechanisms underlying protease regulation in the intestinal tract remains unclear. The objective of this study was to determine microbial regulation of proteolytic activity in intestinal tract using phenotype of post-infection irritable bowel syndrome, a condition characterized by high fecal proteolytic activity. Proteases of host pancreatic origin (chymotrypsin like pancreatic elastase 2A, 3B and trypsin 2) drove proteolytic activity. Of the 14 differentially abundant taxa, high proteolytic activity state was characterized by complete absence of the commensal Alistipes putredinis. Germ free mice had very high proteolytic activity (10-fold of specific-pathogen free mice) which dropped significantly upon humanization with microbiota from healthy volunteers. In contrast, high proteolytic activity microbiota failed to inhibit it, a defect that corrected with fecal microbiota transplant as well as addition of A. putredinis. These mice also had increased intestinal permeability similar to that seen in patients. Microbiota β-glucuronidases mediate bilirubin deconjugation and unconjugated bilirubin is an inhibitor of serine proteases. We found that high proteolytic activity patients had lower urobilinogen levels, a product of bilirubin deconjugation. Mice colonized with β-glucuronidase overexpressing E. coli demonstrated significant inhibition of proteolytic activity and treatment with β-glucuronidase inhibitors increased it. The findings establish that specific commensal microbiota mediates effective inhibition of host pancreatic proteases and maintains intestinal barrier function through the production of β-glucuronidases. This suggests an important homeostatic role for commensal intestinal microbiota.

Project description:Deg proteases are involved in protein quality control and response to stress in prokaryotic organisms. Out of the 16 Deg-encoding genes of Arabidopsis, the products of three, Deg1, Deg5 and Deg8, are located in the thylakoid lumen. Deg1 forms homo-hexamers, degrading photosynthetic proteins, especially during photoinhibition. Deg5 and Deg8 form hetero-complexes, performing apparently similar functions, raising the question whether the two complexes are redundant. To answer this, single, double and triple knockout mutants were generated and their phenotypes were compared. Under optimal growth conditions deg5 and deg8 mutants looked like WT, whereas all combinations of deg1 mutants were smaller and more sensitive to photoinhibition. Under harsher conditions, deg5 and deg8 mutants were also affected, although less than deg1 mutants. Overexpression of Deg5-Deg8 could partially compensate for the loss of Deg1, but only in optimal conditions. Comparative proteomic analysis of deg1 mutants vs. WT revealed moderate up-regulation of thylakoid proteins involved in photoprotection, assembly, repair and house-keeping functions, and down-regulation of all photosynthetic complexes, consistent with the reduced growth of the deg1 mutants. Testing the steady-state level of Deg proteases in WT plants demonstrated that Deg1 was approximately two-fold more abundant than the Deg5-Deg8 complex. Moreover, recombinant Deg1 had higher in vitro proteolytic activity compared with Deg5 and Deg8. Affinity enrichment assays on transgenic plants expressing epitope-tagged Deg proteases revealed that Deg1 was pulled-down almost exclusively, whereas Deg5 and Deg8 were associated with a plethora of thylakoid membrane and lumen proteins, suggesting that they are capable of binding potential substrates, but are unable to degrade them efficiently. Two of the co-precipitated proteins, TL29 and Psb27-H1, were found slightly up-regulated in the triple mutant, suggesting that they are substrates of lumenal Deg proteases. Other pulled-down proteins were the D1 protein, LHCB proteins and subunits of the OEC of PSII, and components of the Cyt b6-f and NADH dehydrogenase complexes, suggesting that these might also be substrates of lumenal Deg proteases. Altogether, the results of this study suggest that differences in abundance and proteolytic activity are the source of the differential importance of the two Deg protease complexes observed in vivo.

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Arabidopsis SBT5.2 and SBT1.7 subtilases mediate C-terminal excision of flg22 epitope from bacterial flagellin

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