Pyroglutamyl peptidase type I from Trypanosoma brucei: a new virulence factor from African trypanosomes that de-blocks regulatory peptides in the plasma of infected hosts

Abstract

Peptidases of parasitic protozoans are emerging as novel virulence factors and therapeutic targets in parasitic infections. A trypanosome-derived aminopeptidase that exclusively hydrolysed substrates with Glp (pyroglutamic acid) in P1 was purified 9248-fold from the plasma of rats infected with Trypanosoma brucei brucei. The enzyme responsible was cloned from a T. brucei brucei genomic DNA library and identified as type I PGP (pyroglutamyl peptidase), belonging to the C15 family of cysteine peptidases. We showed that PGP is expressed in all life cycle stages of T. brucei brucei and is expressed in four other blood-stream-form African trypanosomes. Trypanosome PGP was optimally active and stable at bloodstream pH, and was insensitive to host plasma cysteine peptidase inhibitors. Native purified and recombinant hyper-expressed trypanosome PGP removed the N-terminal Glp blocking groups from TRH (thyrotrophin-releasing hormone) and GnRH (gonadotropin-releasing hormone) with a k(cat)/K(m) value of 0.5 and 0.1 s(-1) x microM(-1) respectively. The half-life of TRH and GnRH was dramatically reduced in the plasma of trypanosome-infected rats, both in vitro and in vivo. Employing an activity-neutralizing anti-trypanosome PGP antibody, and pyroglutamyl diazomethyl ketone, a specific inhibitor of type I PGP, we demonstrated that trypanosome PGP is entirely responsible for the reduced plasma half-life of TRH, and partially responsible for the reduced plasma half-life of GnRH in a rodent model of African trypanosomiasis. The abnormal degradation of TRH and GnRH, and perhaps other neuropeptides N-terminally blocked with a pyroglutamyl moiety, by trypanosome PGP, may contribute to some of the endocrine lesions observed in African trypanosomiasis.

Comparative genomics of canine-isolated Leishmania (Leishmania) amazonensis from an endemic focus of visceral leishmaniasis in Governador Valadares, southeastern Brazil

“…These proteins hydrolyze N-terminal L-pyroglutamyl residues, which confer resistance to the modified peptides from aminopeptidase degradation and in some cases are crucial for biological activity26. A PPI in Trypanosoma brucei has been associated with protection against antimicrobial peptides, suggesting that this enzyme could be an important virulence factor27. However, the corresponding ortholog in L. (L.) major appears to be a key factor during differentiation to metacyclic promastigotes26.…”

Isolation and Characterization of Glutaminyl Cyclases from Drosophila: Evidence for Enzyme Forms with Different Subcellular Localization

“…Presumably, the major function of the pGlu residue is to provide stability against degradation by aminopeptidases, thus prolonging the physiological half-life of these peptides (30). For several hormones, a crucial role of the N-terminus for binding to the respective receptor is described (31).…”

Host-Parasite Interactions in Trypanosomiasis: on the Way to an Antidisease Strategy

“…Quite surprisingly, activation of a T. brucei CP by a kininogen-like molecule from rat serum (called rat trypanopain modulator) has also been reported (69). Recently, the first report of the in vivo activity of bloodstream-released CP has been published with a description of a pyroglutamyl peptidase (PGP) type I from T. brucei brucei (96). In that study, this enzyme showed optimal activity at bloodstream pH and proved to be insensitive to plasma CP inhibitors.…”