p1/s1, a 3’-nucleotidase/nuclease, allows Leishmania major to circumvent host innate immune response mechanisms

3’-nucleotidases/nucleases, distinct class I nucleases of protozoan parasites, play a pivotal role in extracellular purine salvage. As Leishmania are purine auxotrophs and lack de novo synthesis, ectoenzymes facilitating nucleotide and nucleic acid cleavage are indispensable for subsequent uptake. Employing quantitative proteomics, we identified a class I nuclease p1/s1 cluster in L. major that comprises enzymes exhibiting dual 3’-nucleotidase and endonuclease activity. Expression of these enzymes is induced upon miltefosine or staurosporine treatment and was specifically detected in stationary-phase, but not in logarithmic-phase promastigotes.

After confirming secretion of p1/s1, ecto-enzymatic activity was detected on parasites and in the culture supernatant. Viable null mutants deficient for the p1/s1 cluster were only obtained when a diCre-based inducible knockout system was applied, whereas direct deletion approaches were lethal. The viable knockout strains exhibited significantly reduced 3’-nucleotidase/nuclease activity. Notably, these parasites adapted by compensatory enrichment of various alternative purine salvage proteins at the proteomic level.

Furthermore, both enzymatic functions implied mechanisms of host-pathogen interactions to facilitate infection establishment: Utilizing 3’-nucleotidase activity, Leishmania generate extracellular adenosine to suppress inflammatory cytokine secretion from macrophages and reduce lymphocyte proliferation in a human primary cell model. The presence of ecto-nucleases also allowed these parasites to degrade and survive neutrophil extracellular traps, a potent first-line innate immune mechanism in pathogen defense. In summary, our integrative approach combining proteomics, immunological and genome editing methods expands current knowledge about Leishmania major 3’-nucleotidases/nucleases. By offering new insights into the diverse involvements in host-pathogen interactions, we highlight p1/s1 as pivotal factor during infection and potential drug target.