PFPI-like genes are expressed in Leishmania major but are pseudogenes in other Leishmania species.

Pyrococcus furiosus protease I (PFPI) is a multimeric cysteine peptidase from P. furiosus. Genome analyses indicate that orthologues are present in rather few other organisms, including Dictyostelium discoideum and several bacteria, Archaea and plants. An open reading frame (ORF) coding for a PFPI-like protein (PFP1) was identified in Leishmania major and Leishmania mexicana and full-length spliced and polyadenylated PFP1 mRNA detected for both species. Vestiges of a PFPI-like gene could also be identified in Leishmania braziliensis and Leishmania infantum, but no ORF remains owing to the presence of frame-shifts and stop codons. No evidence for a PFPI-like gene could be found in the syntenic region of Trypanosoma brucei or Trypanosoma cruzi, raising the possibility that the PFPI-like genes were acquired by a lateral gene transfer event after the divergence of trypanosomes and Leishmania. The gene may have subsequently degenerated into a pseudogene in some Leishmania species, owing to the loss of relevant biological function. However, antibodies raised against L. mexicana recombinant protein detected PFP1 in promastigote extracts of L. major, but not in L. mexicana promastigote or amastigote extracts. The expression of PFP1 in L. major suggests that PFP1 might contribute to the disease tropism that distinguishes this Leishmania species from others.