Surface localized and extracellular Glyceraldehyde-3-phosphate dehydrogenase of Bacillus anthracis is a plasminogen binding protein

The role of anchorless proteins on the surface of most pathogenic microorganisms has long been studied in context to their interactions with multiple host proteins, facilitating the dissemination of pathogen within the host tissues. In order to gain more insights into anthrax pathogenesis, we hereby report the presence of a prominent moonlighting enzyme, Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) on the surface and in the extracellular medium of Bacillus anthracis. Out of the three heterologously expressed recombinant isoforms, rGapA (334 amino acids in native form; GapA) showed a significant NAD⁺ mediated GAPDH activity, whereas rGapB (342 amino acids in native form; GapB) showed a slight activity with NADP⁺. The rGapN (479 amino acids in native form; GapN) was enzymatically inactive with either NAD⁺ or NADP⁺. GapA was ascertained to be present in the extracellular medium and on the surface of B. anthracis. On the other hand, GapN was absent from both the surface and extracellular medium, whereas GapB was scarcely present on the surface of B. anthracis. Human plasminogen predominantly interacted with the rGapA isoform at physiological concentrations and the interaction was found to be lysine dependent. Immunization with rGapA resulted in a significant protection upon challenge with Bacillus anthracis in the murine model.