title: Developmentally regulated expression of a cell surface class I nuclease in Leishmania mexicana.
abstract: Leishmania mexicana, like other trypanosomatid parasites, is a purine auxotroph and must obtain these essential nutrients from its sandfly and mammalian hosts. A single copy gene encoding its unique externally oriented, surface membrane, purine salvage enzyme 3'-nucleotidase/nuclease, was isolated. Structural features of the deduced protein included: an endoplasmic reticulum-directed signal peptide, several conserved class I catalytic and metal co-factor (Zn(2+)) binding domains, transmembrane anchor sequence and a C-terminal cytoplasmic tail. 3'-Nucleotidase/nuclease gene (mRNA) and protein (enzyme activity) expression were examined in three different L. mexicana developmental forms: procyclic promastigotes, metacyclic promastigotes and amastigotes. Results of both approaches demonstrated that the 3'-nucleotidase/nuclease was a stage-specific enzyme, being expressed by promastigote forms (stages restricted to the insect vector), but not by amastigotes (which produce disease in mammalian hosts). Starvation of these parasites for purines resulted in the significant up-regulation of both 3'-nucleotidase/nuclease mRNA and enzyme activity in promastigotes, but not in amastigotes. These results underscore the critical role that the 3'-nucleotidase/nuclease must play in purine salvage during the rapid multiplicative expansion of the parasite population within its insect vector. To our knowledge, the L. mexicana 3'-nucleotidase/nuclease is the first example of a nutrient-induced and developmentally regulated enzyme in any parasitic protozoan.
authors.affiliation: Division of Molecular Biology and Immunology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK.
authors.forename: William F
authors.initials: WF
authors.lastname: Sopwith
authors.forename: Alain
authors.initials: A
authors.lastname: Debrabant
authors.forename: Mat
authors.initials: M
authors.lastname: Yamage
authors.forename: Dennis M
authors.initials: DM
authors.lastname: Dwyer
authors.forename: Paul A
authors.initials: PA
authors.lastname: Bates
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003470:Culture Media; D015971:Gene Expression Regulation, Enzymologic; D007894:Leishmania mexicana / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*; D008018:Life Cycle Stages; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009708:Nucleotidases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011687:Purines / Q000378:metabolism; D017422:Sequence Analysis, DNA
chemical_list: D003470:Culture Media; D011687:Purines; D009708:Nucleotidases; C040470:3'-nucleotidase; C030985:purine