Abstract
All species of Leishmania express a major surface protease (Msp or gp63) that facilitates the interactions of the parasite with its environment at several steps in its life cycle. The msp gene family in Leishmania chagasi contains three classes of genes whose mRNAs are differentially expressed during parasite growth. Logarithmic phase (low infectivity) promastigotes express only 63-kDa versions of Msp, whereas stationary phase (high infectivity) promastigotes express both 63- and 59-kDa Msps. The different migrations of the 59- and 63-kDa proteins on acrylamide gels are not due to differences in N-linked glycosylation or the membrane anchor. Plasmid transfections of Leishmania demonstrate that mspS2 of the stationary gene class encodes a 59-kDa protein. Expression of the 59-kDa protein in stationary phase promastigotes ceases after about 12 weeks of in vitro cultivation when the parasites become attenuated. Attenuated parasites can be stimulated to re-express the 59-kDa Msp by passage through mice followed by several in vitro passages of recovered promastigotes. Amastigotes express yet another subset of Msp proteins. Thus, the 59-kDa product of mspS2 is expressed only in stationary phase promastigotes and only after recent exposure to environmental changes encountered in the mammalian host cell.
Highlights
All species ofLeishmania express a major surface protease (Msp or gp63) that facilitates the interactions of the parasite with its environment at several steps in its life cycle
The sequence of one gene expressed in logarithmic growth phase, mspL1, has been determined, and its product is identical to Msp81 except for two amino acid substitutions [23]
We previously demonstrated that long term cultivation of virulent L. chagasi promastigotes in liquid culture consistently results in their conversion to attenuated parasites that have 5-30% of the infectivity at stationary phase compared with virulent parasites (Ref. 24 and data not shown)
Summary
All species ofLeishmania express a major surface protease (Msp or gp63) that facilitates the interactions of the parasite with its environment at several steps in its life cycle. Abbreviations for this molecule include gp (for 63-kDa glycoprotein) [5], psp (for promastigote surface protease) [6], or Msp (for major surface protease) [7] We refer to this family of surface proteases as Msp since, as shown here, Leishmania chagasi promastigotes and amastigotes possess different forms of the protein. Msp is a zinc protease with a broad substrate specificity and a wide pH optimum [13, 14] Both the promastigote and amastigote stages of the parasite express Msp proteins [10, 15, 16], but at least in Leishmania major the promastigote expresses much higher amounts [17]. The stationary genes (mspS) are expressed only in stationary growth phase by virulent promastigotes, and the log genes
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