Mammalian-like type II glutaminyl cyclases in Porphyromonas gingivalis and other oral pathogenic bacteria as targets for treatment of periodontitis.

The development of a targeted therapy would significantly improve the treatment of periodontitis and its associated diseases including Alzheimer Disease, rheumatoid arthritis, and cardiovascular diseases. Glutaminyl cyclases (QCs) from the oral pathogens Porphyromonas gingivalis, Tannerella forsythia and Prevotella intermedia represent attractive target enzymes for small-molecule inhibitor development, as their action is likely to stabilize essential periplasmic and outer membrane proteins by N-terminal pyroglutamination. In contrast to other microbial QCs that utilize so-called type I enzymes, these oral pathogens possess sequences corresponding to type II QCs, observed hitherto only in animals. However, whether differences between these bacteroidal QCs and animal QCs are sufficient to enable development of selective inhibitors is not clear. To learn more, we recombinantly expressed all three QCs. They exhibit comparable catalytic efficiencies and are inhibited by metal chelators. Crystal structures  of the enzymes from P. gingivalis (PgQC) and T. forsythia (TfQC) reveal a tertiary structure composed of an eight-stranded ß-sheet surrounded by seven α-helices, typical of animal type II QCs. In each case, an active site Zn ion is tetrahedrally coordinated by conserved residues. Nevertheless, significant differences to mammalian enzymes are found around the active site of the bacteroidal enzymes. Application of a PgQC-selective inhibitor described here for the first time results in growth inhibition of two P. gingivalis clinical isolates in a dose dependent manner. The insights gained by these studies will assist in the development of highly specific small-molecule bacteroidal QC inhibitors, paving the way for alternative therapies against periodontitis and associated diseases.

Mammalian-like type II glutaminyl cyclases in Porphyromonas gingivalis and other oral pathogenic bacteria as targets for treatment of periodontitis.

The development of a targeted therapy would significantly improve the treatment of periodontitis and its associated diseases including Alzheimer's disease, rheumatoid arthritis, and cardiovascular diseases. Glutaminyl cyclases (QCs) from the oral pathogens Porphyromonas gingivalis, Tannerella forsythia, and Prevotella intermedia represent attractive target enzymes for small-molecule inhibitor development, as their action is likely to stabilize essential periplasmic and outer membrane proteins by N-terminal pyroglutamination. In contrast to other microbial QCs that utilize the so-called type I enzymes, these oral pathogens possess sequences corresponding to type II QCs, observed hitherto only in animals. However, whether differences between these bacteroidal QCs and animal QCs are sufficient to enable development of selective inhibitors is not clear. To learn more, we recombinantly expressed all three QCs. They exhibit comparable catalytic efficiencies and are inhibited by metal chelators. Crystal structures of the enzymes from P. gingivalis (PgQC) and T. forsythia (TfQC) reveal a tertiary structure composed of an eight-stranded ß-sheet surrounded by seven α-helices, typical of animal type II QCs. In each case, an active site Zn ion is tetrahedrally coordinated by conserved residues. Nevertheless, significant differences to mammalian enzymes are found around the active site of the bacteroidal enzymes. Application of a PgQC-selective inhibitor described here for the first time results in growth inhibition of two P. gingivalis clinical isolates in a dose-dependent manner. The insights gained by these studies will assist in the development of highly specific small-molecule bacteroidal QC inhibitors, paving the way for alternative therapies against periodontitis and associated diseases.

Purification and characterisation of recombinant His-tagged RgpB gingipain from Porphymonas gingivalis.

Gingipain proteases are important virulence factors from the periodontal pathogen Porphyromonas gingivalis and are the target of many in vitro studies. Due to their close biochemical properties, purification of individual gingipains is difficult and requires multiple chromatographic steps. In this study, we demonstrate that insertion of a hexahistidine affinity tag upstream of a C-terminal outer membrane translocation signal in RgpB gingipain leads to the secretion of a soluble, mature form of RgpB bearing the affinity tag that can easily be purified by nickel-chelating affinity chromatography. The final product obtained high yielding high purity is biochemically indistinguishable from the native RgpB enzyme.

The outer-membrane export signal of Porphyromonas gingivalis type IX secretion system (T9SS) is a conserved C-terminal ß-sandwich domain.

In the recently characterized Type IX Secretion System (T9SS), the conserved C-terminal domain (CTD) in secreted proteins functions as an outer membrane translocation signal for export of virulence factors to the cell surface in the Gram-negative Bacteroidetes phylum. In the periodontal pathogen Porphyromonas gingivalis, the CTD is cleaved off by PorU sortase in a sequence-independent manner, and anionic lipopolysaccharide (A-LPS) is attached to many translocated proteins, thus anchoring them to the bacterial surface. Here, we solved the atomic structure of the CTD of gingipain B (RgpB) from P. gingivalis, alone and together with a preceding immunoglobulin-superfamily domain (IgSF). The CTD was found to possess a typical Ig-like fold encompassing seven antiparallel ß-strands organized in two ß-sheets, packed into a ß-sandwich structure that can spontaneously dimerise through C-terminal strand swapping. Small angle X-ray scattering (SAXS) revealed no fixed orientation of the CTD with respect to the IgSF. By introducing insertion or substitution of residues within the inter-domain linker in the native protein, we were able to show that despite the region being unstructured, it nevertheless is resistant to general proteolysis. These data suggest structural motifs located in the two adjacent Ig-like domains dictate the processing of CTDs by the T9SS secretion pathway.