Secretory nucleoside diphosphate kinase from both the intra-and extra-cellular pathogenic bacteria are functionally indistinguishable

Abstract

Nucleoside diphosphate kinase (NDK), responsible for the maintenance of NTP pools, is an ATP utilizing enzyme secreted by different pathogens. We found that NDK from Salmonella enterica serovar typhimurium is also secretory in nature. Secretory NDK is known to play a crucial role in the survival of pathogenic microbes within host cells through their interaction with extracellular-ATP. To elucidate this aspect, we assessed the contribution of secretory products containing NDK from intra-cellular (M. tuberculosis and S. typhimurium) or extra-cellular (V. cholerae) pathogens in the process of ATP-induced J774 mouse macrophage cell lysis by monitoring lactate dehydrogenase (LDH) release in the culture medium. Compared to untreated control, our results demonstrate that S. typhimurium secretory products caused > 2 fold decrease in LDH release from J774 macrophage cells treated with ATP. Furthermore, the secretory products from ndk-deleted strain of S. typhimurium did not display such behavior. Contrary to this observation, the secretory products containing NDK of Vibrio cholerae was found to be cytotoxic to J774 cells. At amino acid level, sequences of both the NDKs (S. typhimurium/V. cholerae) exhibited 65% identity and their biochemical characteristics (autophosphorylation/phosphotransfer activities) were indistinguishable. However, to our surprise, secretory product of a ndk-deleted strain of S. typhimurium when complemented with V. cholerae ndk was able to prevent ATP-induced cytolysis. Taken together, our results unambiguously insinuate that intrinsic properties of secretory NDK is identical in intra-and extra-cellular pathogens irrespective of their mode of manifestation.