Periodontitis is an inflammatory disease of the supporting structures of the teeth caused by, among other pathogens, Prevotella intermedia. Many strains of P. intermedia are resistant to killing by the human complement system, which is present at up to 70% of serum concentration in gingival crevicular fluid. Incubation of human serum with recombinant cysteine protease of P. intermedia (interpain A) resulted in a drastic decrease in bactericidal activity of the serum. Furthermore, a clinical strain 59 expressing interpain A was more serum-resistant than another clinical strain 57, which did not express interpain A, as determined by Western blotting. Moreover, in the presence of the cysteine protease inhibitor E64, the killing of strain 59 by human serum was enhanced. Importantly, we found that the majority of P. intermedia strains isolated from chronic and aggressive periodontitis carry and express the interpain A gene. The protective effect of interpain A against serum bactericidal activity was found to be attributable to its ability to inhibit all three complement pathways through the efficient degradation of the α-chain of C3—the major complement factor common to all three pathways. P. intermedia has been known to co-aggregate with P. gingivalis, which produce gingipains to efficiently degrade complement factors. Here, interpain A was found to have a synergistic effect with gingipains on complement degradation. In addition, interpain A was able to activate the C1 complex in serum, causing deposition of C1q on inert and bacterial surfaces, which may be important at initial stages of infection when local inflammatory reaction may be beneficial for a pathogen. Taken together, the newly characterized interpain A proteinase appears to be an important virulence factor of P. intermedia.

SUMMARY The Gram-negative oral anaerobe Prevotella intermedia forms an iron(III) protoporphyrin IX pigment from haemoglobin. The microorganism expresses a 90 kDa cysteine protease, Interpain A (InpA), a homologue of Streptococcus pyogenes streptopain (SpeB). The role of InpA in haemoglobin breakdown and haem release was investigated. At pH 7.5, InpA mediated oxidation of oxyhaemoglobin to hydroxymethaemoglobin (in which the haem iron is oxidised to the Fe(III) state and which carries OH− as the sixth co-ordinate ligand) by limited proteolysis of globin chains as indicated by SDS-PAGE and MALDI-TOF analysis. Prolonged incubation at pH 7.5, did not result in further haemoglobin protein breakdown, but in the formation of a haemoglobin haemichrome (where the haem Fe atom is co-ordinated by another amino acid ligand in addition to the proximal histidine) stable to degradation by InpA. InpA-mediated haem release from hydroxymethaemoglobin-agarose was minimal compared with trypsin at pH 7.5. At pH 6.0, InpA increased oxidation at a rate greater than auto-oxidation, producing aquomethaemoglobin (with H2O as sixth co-ordinate ligand), and resulted in its complete breakdown and haem loss. Aquo-methaemoglobin proteolysis and haem release was prevented by blocking haem dissociation by ligation with azide, whilst InpA proteolysis of haem-free globin was rapid even at pH 7.5. Both oxidation of oxyhaemoglobin and breakdown of methaemoglobin by InpA were inhibited by the cysteine-protease inhibitor E64. In summary we conclude that InpA may play a central role in haem acquisition by mediating oxyhaemoglobin oxidation, and by degrading aquomethaemoglobin in which haem-globin affinity is weakened under acidic conditions.

Prevotella intermedia is a major periodontopathogen contributing to human gingivitis and periodontitis. Such pathogens release proteases as virulence factors that cause deterrence of host defenses and tissue destruction. A new cysteine protease from the cysteine-histidine-dyad class, interpain A, was studied in its zymogenic and self-processed mature forms. The latter consists of a bivalved moiety made up by two subdomains. In the structure of a catalytic cysteine-to-alanine zymogen variant, the right subdomain interacts with an unusual prodomain, thus contributing to latency. Unlike the catalytic cysteine residue, already in its competent conformation in the zymogen, the catalytic histidine is swung out from its active conformation and trapped in a cage shaped by a backing helix, a zymogenic hairpin, and a latency flap in the zymogen. Dramatic rearrangement of up to 20 Å of these elements triggered by a tryptophan switch occurs during activation and accounts for a new activation mechanism for proteolytic enzymes. These findings can be extrapolated to related potentially pathogenic cysteine proteases such as Streprococcus pyogenes SpeB and Porphyromonas gingivalis periodontain. Periodontal disease (PD)5 affects the tissues that surround and support the teeth and may lead to loosening and eventual loss of teeth if untreated. It is caused by bacteria and affects mildly 90% and severely 10% of the population worldwide (1, 2). In addition, symptoms of PD appear in a series of systemic diseases due to its inflammatory and infective character (2, 3). Present day treatment and curettage of severe PD includes the mechanical cleansing of the affected area and is efficient in general. However, it is costly, time consuming, and painful and needs frequent repetition. In addition, it may entail the indiscriminate usage of antibiotics, which contributes to the spread of antibiotic-resistant strains (2, 4). Consequently, there is a need for innovative and specific therapeutic approaches against PD.Prevotella intermedia is a major bacterial periodontal pathogen in humans together with Porphyromonas gingivalis, among others (5, 6). Such bacteria colonize the gingival crevice and produce virulence factors that cause disease. Bacterial infection leads to the bacterial secretion or induction of host overproduction of proteolytic enzymes such as bacterial collagenases, matrix metalloproteases, and serine and cysteine proteases (CPs) (2, 7, 8). These proteases destroy host tissue and compromise host defenses. In addition, proteases may give rise to fibrinolytic activity and inactivate components of the bloodcoagulation cascade such as the protease inhibitors, ␣ 1 -proteinase inhibitor and ␣ 2 -macroglobulin. Proteolysis further covers alimentary requirements, because most of bacterial nutrition is obtained from degraded periodontal tissue and tissue fluid (9).Most studies on the bacterial proteolytic armamentarium in PD have been performed with P. gingivalis (9). In contrast, the factors governing P. intermedia infection, a black-pig...

Treponema denticola is a major pathogen of chronic periodontitis. Analysis of the T. denticola genome revealed a gene orthologous with a gene encoding a cysteine protease from Streptococcus pyogenes (IdeS). IdeS interferes with IgG-dependent opsonophagocytosis by specific cleavage of IgG molecules. Analysis of this gene (termed ideT) revealed it to encode a two domain protein. The N-terminus of this protein is composed of a tandem, immunoglobulin-like domain, followed by a C-terminally located IdeS-like protease domain. We show here that during secretion the IdeT protein is processed into an N-terminal fragment which remains associated with the cell, and a C-terminal portion released into the medium. Although this secreted domain of IdeT, termed dentipain, shows only 25% identity with the IdeS protease, the putative catalytic cysteine and histidine residues are strongly conserved. Analysis of recombinant dentipain revealed that it cleaved the insulin β-chain, an activity which was inhibited by E-64, a diagnostic inhibitor of cysteine proteases. Apart from insulin no cleavage of other protein substrates was detected, suggesting that dentipain has oligopeptidase activity. A mutant strain was constructed bearing a modified ideT whose dentipain domain was deleted. This mutant was found to be significantly reduced in its abscess forming activity compared to the parental strain in a murine abscess model, suggesting that dentipain contributes to the virulence of T. denticola.

Periodontitis is an inflammatory disease of the supporting structures of the teeth caused by, among other pathogens, Prevotella intermedia. Many strains of P. intermedia are resistant to killing by the human complement system, which is present at up to 70% of serum concentration in gingival crevicular fluid. Incubation of human serum with recombinant cysteine protease of P. intermedia (interpain A) resulted in a drastic decrease in bactericidal activity of the serum. Furthermore, a clinical strain 59 expressing interpain A was more serum-resistant than another clinical strain 57, which did not express interpain A, as determined by Western blotting. Moreover, in the presence of the cysteine protease inhibitor E64, the killing of strain 59 by human serum was enhanced. Importantly, we found that the majority of P. intermedia strains isolated from chronic and aggressive periodontitis carry and express the interpain A gene. The protective effect of interpain A against serum bactericidal activity was found to be attributable to its ability to inhibit all three complement pathways through the efficient degradation of the a-chain of C3-the major complement factor common to all three pathways. P. intermedia has been known to co-aggregate with P. gingivalis, which produce gingipains to efficiently degrade complement factors. Here, interpain A was found to have a synergistic effect with gingipains on complement degradation. In addition, interpain A was able to activate the C1 complex in serum, causing deposition of C1q on inert and bacterial surfaces, which may be important at initial stages of infection when local inflammatory reaction may be beneficial for a pathogen. Taken together, the newly characterized interpain A proteinase appears to be an important virulence factor of P. intermedia.