Outer membrane vesicle proteome of Aggregatibacter actinomycetemcomitans serotype e strain 173

Aggregatibacter actinomycetemcomitans is an oral and systemic pathogen associated with aggressive forms of periodontitis, and with endocarditis. Outer membrane vesicles (OMVs) released by this species have been demonstrated to deliver effector proteins such as cytolethal distending toxin (CDT) and leukotoxin (LtxA) into human host cells, and to act as triggers of innate immunity upon carriage of NOD1- and NOD2-active pathogen-associated molecular patterns (PAMPs). To improve our understanding of the pathogenicity-associated functions that A. actinomycetemcomitans exports via OMVs, we have used liquid chromatography-tandem mass spectrometry (LC-MS/MS) to characterize the OMV-associated proteome of a rough-colony type clinical isolate, strain 173 (serotype e). This yielded identification of 151 proteins overlapping in three out of four independent experiments, using density gradient-purified OMVs. Further to confirming the vesicle-associated release of LtxA, and of several proteins earlier demonstrated to act as immunoreactive antigens in the human host, we identified numerous additional putative virulence-related proteins in the A. actinomycetemcomitans OMV proteome, including proteins involved in immune evasion, drug targeting, and iron/nutrient acquisition. In summary our findings are consistent with an OMV-associated proteome that exhibits several offensive and defensive functions, and they provide a comprehensive basis to further disclose roles of A. actinomycetemcomitans OMVs in periodontal and systemic disease.