Abstract
Oral streptococci are a heterogeneous group of human commensals, with a potential to cause serious infections. Activation of plasminogen has been shown to increase the virulence of typical human pathogenic streptococci such as S. pneumoniae. One important factor for plasminogen activation is the streptococcal α-enolase. Here we report that plasminogen activation is also common in oral streptococci species involved in clinical infection and that it depends on the action of human plasminogen activators. The ability to activate plasminogen did not require full conservation of the internal plasminogen binding sequence motif FYDKERKVY of α-enolase that was previously described as crucial for increased plasminogen binding, activation and virulence. Instead, experiments with recombinant α-enolase variants indicate that the naturally occurring variations do not impair plasminogen binding. In spite of these variations in the internal plasminogen binding motif oral streptococci showed similar activation of plasminogen. We conclude that the pathomechanism of plasminogen activation is conserved in oral streptococci that cause infections in human. This may contribute to their opportunistic pathogenic character that is unfurled in certain niches.
Highlights
Oral streptococci are commensal microorganisms that may exert beneficial probiotic effects when residing at their natural habitat, the oral cavity
Bound proteins were eluted from the surface of the bacteria, separated by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) (Fig. 1), and identified by either MALDI-TOF-MS or by immunoblot analysis. This experiment identified three major ligands bound by S. oralis isolate SV11: serum albumin, immunoglobulin G (IgG), and plasminogen
In which S. oralis isolate SV11 was incubated with a solution of purified human plasminogen demonstrated its direct interaction with the bacterial surface indicating that the binding does not depend on other factors from human plasma (Fig. 1)
Summary
Oral streptococci are commensal microorganisms that may exert beneficial probiotic effects when residing at their natural habitat, the oral cavity. Despite considerable pathogenic potential of the causative organisms and the clinical relevance of infections with oral streptococci, their molecular pathogenesis is barely understood. Some of their pathogenic actions may be unique to oral streptococci, while others may show high similarity to those of the more extensively studied streptococci. The latter very often use the host plasminogen system in order to invade tissues and establish an infection. We have comprehensively investigated the influence of natural variations on plasminogen binding and overall activation of plasminogen by oral streptococci
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