ABSTRACT
A membrane-bound proteinase is expressed at the surface of Leishmania promastigotes, and has been called the promastigote surface proteinase (PSP). Prior to its identification as an active proteolytic enzyme (a zinc metalloproteinase, see below), the ‘major surface antigen’ of the promastigote was called p63 or gp63. PSP has been shown to occur at the surface of all species of Leishmania that have been examined (Bouvier et al., 1987; Etges, unpublished) and, although it appears to be expressed at low levels by the amastigote from an abundant, constitutively transcribed mRNA (Button et at., 1989; Wilson and Hardin, 1990), the results of efforts to demonstrate the presence of the active protease at the surface of amastigotes have been negative or inconclusive. Independent of its proteolytic activity, PSP has been identified as the major complement component 3 (C3) acceptor of Leishmania mexicana promastigotes (Russell, 1987) and to be involved, either directly or via bound C3, in the attachment of the promastigote to the host macrophage (Russell and Wilhelm, 1986). The proteolytic shedding of C3 fragments from opsonized L. donovani promastigotes could, however, involve the activity of PSP (Puentes et al., 1989).
