HtrA--a renaissance protein

The role of proteases and inflammatory molecules in triggering neovascular age-related macular degeneration: basic science to clinical relevance

Age-related macular degeneration (AMD) causes severe vision impairment in aged individuals. The health impact and cost of the disease will dramatically increase over the years, with the increase in the aging population. Currently, antivascular endothelial growth factor agents are routinely used for managing late-stage AMD, and recent data have shown that up to 15%-33% of patients do not respond to this treatment. Henceforth, there is a need to develop better treatment options. One avenue is to investigate the role proteases and inflammatory molecules might have in regulating and being regulated by vascular endothelial growth factor. Moreover, emerging data indicate that proteases and inflammatory molecules might be critical in the development and progression of AMD. This article reviews recent literature that investigates proteases and inflammatory molecules involved in the development of AMD. Gaining insights into the proteolytic and inflammatory pathways associated with the pathophysiology of AMD could enable the development of additional or alternative drug strategies for the treatment of AMD.

HtrA in Porphyromonas gingivalis can regulate growth and gingipain activity under stressful environmental conditions

In several micro-organisms, HtrA, a serine periplasmic protease, is considered an important virulence factor that plays a regulatory role in oxidative and temperature stress. The authors have previously shown that the vimA gene product is an important virulence regulator in Porphyromonas gingivalis. Further, purified recombinant VimA physically interacted with the major gingipains and the HtrA from P. gingivalis. To further evaluate a role for HtrA in the pathogenicity of this organism, a 1.5 kb fragment containing the htrA gene was PCR-amplified from the chromosomal DNA of P. gingivalis W83. This gene was insertionally inactivated using the ermF-ermAM antibiotic-resistance cassette and used to create an htrA-deficient mutant by allelic exchange. In one randomly chosen isogenic mutant designated P. gingivalis FLL203, there was increased sensitivity to hydrogen peroxide. Growth of this mutant at an elevated temperature was more inhibited compared to the wild-type. Further, in contrast to the wild-type, there was a significant decrease in Arg-gingipain activity after heat shock in FLL203. However, the gingipain activity in the mutant returned to normal levels after a further 30 min incubation at room temperature. Collectively, these data suggest that HtrA may play a similar role in oxidative and temperature stress in P. gingivalis as observed in other organisms.

Wolbachia endosymbionts of Onchocerca volvulus express a putative periplasmic HtrA-type serine protease

Wolbachia are intracellular bacteria of many filarial nematodes. A mutualistic interaction between the endobacteria and the filarial host is likely, because the clearance of Wolbachia by tetracycline leads to the obstruction of embryogenesis and larval development. Databases were searched for exported molecules to identify candidates involved in this mutualism. Fragments of a Wolbachia serine protease from the human filarial parasite Onchocerca volvulus were obtained (Wol-Ov-HtrA) by the use of a PCR technique and primers based on the Rickettsia prowazekii genome. The deduced amino acid sequence exhibited 87% and 81% identity to the homologous Wolbachia proteases identified from Brugia malayi and Drosophila melanogaster, respectively. The full-length cDNA encodes 494 amino acids with a calculated mass of 54 kDa. Three characteristic features, (i) a catalytic triad of serine proteases, (ii) two PDZ domains and (iii) a putative signal peptide, classify the endobacterial protein as a member of the periplasmic HtrA family of proteases known to express chaperone and regulator activity of apoptosis. Using a rabbit antiserum raised against a recombinantly expressed 33-kDa fragment of Wol-Ov-HtrA, strong labelling of the antigen was found associated with endobacteria in hypodermis, oocytes, zygotes, all embryonic stages and microfilariae of O. volvulus. Staining of hypodermal cytoplasm surrounding the endobacteria indicated a possible release of the protein from the Wolbachia. The demonstration of Wol-Ov-HtrA-reactive IgG1 antibodies in sera of O. volvulus-infected persons indicated the exposure to the protein and its recognition by the human immune system. Wol-Ov-HtrA is a candidate for an exported Wolbachia protein that may interact with the filarial host metabolism.

Mammalian mitochondrial IAP binding proteins

Four mitochondrial proteins have been identified that immunoprecipitate with the mammalian inhibitor of apoptosis (IAP) protein XIAP. Each of them interacts via a processed amino terminus that resembles those of the insect pro-apoptotic IAP binding proteins Grim, HID, Reaper, and Sickle. Two, Diablo/Smac and HrtA2/Omi, have been extensively characterized. Both Diablo and HtrA2 can bind to IAPs and promote apoptosis when over-expressed in transfected cells, but unlike the insect IAP antagonists, to date there is scant evidence that they are important regulators of apoptosis in more physiological circumstances.