Expanded substrate specificity supported by P1' and P2' residues enables bacterial dipeptidyl-peptidase 7 to degrade bioactive peptides

Potential elevation of exopeptidase activity of Glu-specific endopeptidase I/GluV8 mediated by hydrophobic P1'-position amino acid residue

We recently reported that the activities of dipeptidyl-peptidase (DPP)7 and DPP11, S46-family exopeptidases were significantly elevated by the presence of prime-side amino acid residues of substrates caused by an increase in kcat [Ohara-Nemoto Y. et al., J Biol Chem 298(3):101585. doi: 10.1016/j.jbc.2022]. In the present study, the effects of prime-side residues on Glu-specific endopeptidase I/GluV8 from Staphylococcus aureus were investigated using a two-step cleavage method with tetrapeptidyl-methycoumaryl-7-amide (MCA) carrying P2- to P2'-position residues coupled with DPP11 as the second enzyme. GluV8 showed maximal activity toward benzyloxycarbonyl (Z)-LLE-MCA, while the effects of hydrolysis of substrates one residue shorter, such as acetyl (Ac)-Val-Glu- and Leu-Glu-MCA, were negligible. Nevertheless, activity towards Ac-VE-|-ID-MCA, a substrate carrying P1' and P2' residues, emerged and reached a level 44 % of that for Z-LLE-MCA. Among 11 Ac-HAXD-MCA (X is a varied amino acid), the highest level of activity enhancement was achieved with P1'-Leu and Ile, followed by Phe, Val, Ser, Tyr, and Ala, while Gly and Lys showed scant effects. This activation order was in parallel with the hydrophobicity indexes of these amino acids. The prime-side residues increased kcat/KM primarily through a maximum 500-fold elevation of kcat as well as S46-family exopeptidases. The MEROPS substrate database also indicates a close relationship between activity and hydrophobicity of the P1' residues in 93 N-terminal-truncated substrates, though no correlation was observed among all 4328 GluV8 entities examined. Taken together, these results are the first to demonstrate N-terminal exopeptidase activity of GluV8, considered to be prompted by hydrophobic P1' amino acid residues.

Dipeptidyl-Peptidase-4 and Glucagon-like-Peptide-1, a Link in the Connection between Periodontitis and Diabetes Mellitus-What Do We Know So Far?-A Scoping Review

Periodontitis is a common condition affecting the tissues surrounding and supporting teeth. In addition to oral health concerns, periodontal disease increases the chance of developing systemic illnesses including type 2 diabetes mellitus. Porphyromonas gingivalis, a key-stone pathogen that has been linked to the pathophysiology of periodontal disease, can generate a series of dipeptide producing exopeptidases, dipeptidyl peptidases (DPP). DPP-4 levels in gingival crevicular fluid have been shown to increase during active periodontal disease, which may lead to their association with the disease's progression. Following oral glucose administration, mice injected with DPP-4 had higher blood glucose than the control group. DPP-4 inhibitors are used to treat patients with type 2 diabetes mellitus in order to extend the half-life of incretins. Elevated glucagon-like peptide-1 (GLP-1) levels following periodontal therapy could be considered new and applicable real-world evidence confirming the experimental findings of a beneficial interaction between oral microbiota and incretin axis. GLP-1 receptor agonist exendin-4 enhanced the osteoblast proliferation and development of these stem cells and inhibited the effects of glucose on the cells. In addition to lowering blood sugar, liraglutide, a GLP-1 receptor agonist, also possesses anti-inflammatory and bone-protective properties. These findings support the use of GLP-1 in the management and prevention of diabetic periodontitis.

The Bacteroidetes Q-rule and glutaminyl cyclase activity increase the stability of extracytoplasmic proteins

IMPORTANCE

Exclusively in the Bacteroidetes phylum, most proteins exported across the inner membrane via the Sec system and released into the periplasm by type I signal peptidase have N-terminal glutamine converted to pyroglutamate. The reaction is catalyzed by the periplasmic enzyme glutaminyl cyclase (QC), which is essential for the growth of Porphyromonas gingivalis and other periodontopathogens. Apparently, pyroglutamyl formation stabilizes extracytoplasmic proteins and/or protects them from proteolytic degradation in the periplasm. Given the role of P. gingivalis as the keystone pathogen in periodontitis, P. gingivalis QC is a promising target for the development of drugs to treat and/or prevent this highly prevalent chronic inflammatory disease leading to tooth loss and associated with severe systemic diseases.

Immunoelectron Microscopic Analysis of Dipeptidyl-Peptidases and Dipeptide Transporter Involved in Nutrient Acquisition in Porphyromonas gingivalis

Porphyromonas gingivalis is an asaccharolytic, Gram-negative, anaerobic bacterium representing a keystone pathogen in chronic periodontitis. The bacterium's energy production depends on the metabolism of amino acids, which are predominantly incorporated as dipeptides via the proton-dependent oligopeptide transporter (Pot). In this study, the localization of dipeptidyl-peptidases (DPPs) and Pot was investigated for the first time in P. gingivalis using immunoelectron microscopy with specific antibodies for the bacterial molecules and gold-conjugated secondary antibodies on ultrathin sections. High-temperature protein G and hemin-binding protein 35 were used as controls, and the cytoplasmic localization of the former and outer membrane localization of the latter were confirmed. P. gingivalis DPP4, DPP5, DPP7, and DPP11, which are considered sufficient for complete dipeptide production, were detected in the periplasmic space. In contrast, DPP3 was localized in the cytoplasmic space in accord with the absence of a signal sequence. The inner membrane localization of Pot was confirmed. Thus, spatial integration of the nutrient acquisition system exists in P. gingivalis, in which where dipeptides are produced in the periplasmic space by DPPs and readily transported across the inner membrane via Pot.

Novel hit of DPP-4Is as promising antihyperglycemic agents with dual antioxidant/anti-inflammatory effects for type 2 diabetes with/without COVID-19

DPP-4Is are well recognized therapy for type 2 diabetes. In spite of sharing a common mode of action, the chemical diversity among members of DPP-4Is raised the question whether structural differences may result in distinguished activities. DPP-4Is were recently explored as drug repurposing means for treatment of SARS-CoV-2 due to the urgent need for small molecule drugs for controlling infections. The use of DPP-4Is was not correlated with adverse COVID-19-related consequences among patients with type 2 diabetes. Inspired by these reasons and the importance of pyrimidinone ring as DPP-4I with both antioxidant and anti-inflammatory activities, we succeeded to prepare some novel pyrimidinone and thio-pyrimidinone derivatives, which were then screened for their antidiabetic activity and DPP-4 inhibition. In addition, their anti-inflammatory effect on LPS-stimulated RAW 264.7 cells were evaluated. Furthermore, their antioxidant activities were also tested.