The Type 2 secretion system (T2SS) is a ubiquitously distributed molecular machine found in pathogenic Gram-negative bacteria involved in the interactions of a wide range of substrates from the periplasm. A subset of exported substrates plays a key role in bacterial pathogenesis and are involved in infection processes such as: adhesion, pathogenicity, host adaptation and intracellular survival. Currently, many published studies focus on the structural and functional analysis of the protein complex of the T2SS. However, the functional role and mechanism for the exported substrates of this secretion system and its role in virulence is not fully understood.
The protein secretin-PulD-is a crucial accessory component of the T2SS as its absence prevents the release of translocated substrates into the extracellular space. Using the clinical isolate Klebsiella pneumoniae AJ218 as a model, previous experiments hinted that PulD may play a role in stimulating macrophage cell death, and the T2SS may associate with the bacterial virulence.
To further confirm the damage effect of secreted substrates, the pullulanase PulA was chosen for this study because it is the only distinct lipoprotein secreted by K. pneumoniae T2SS. In this study, we investigate the putative lipoprotein PulA and its role in K. pneumoniae virulence through colony forming unit -macrophage (CFU-M) clonogenic assay. Better understanding of this suspected substrate lipoprotein could reveal greater understanding of the virulence strategies employed by other pathogenic organisms with T2SS with similar substrates.