Structural insights into thioredoxin-2: a component of malaria parasite protein secretion machinery

Abstract

Thioredoxins are vital components of Plasmodium proteome and act as both reducing agents and protein disulfide reductases. The malaria parasite P. falciparum thioredoxin-2 (PfTrx-2) is part of the multi-protein complex embedded within the parasite parasitophorous vacuolar membrane (PVM) which purportedly directs protein secretion. We have characterized structural and enzymatic features of PfTrx-2, and we show that PfTrx-2 adopts a canonical thioredoxin fold but with significant structural differences in its N-terminus. Our confocal localization data suggest distinct PVM residency of PfTrx-2. Based on the crystal structure of PfTrx-2, we screened and tested small molecule drug-like libraries for compounds which target unique structural features of PfTrx-2. Disruption of PfTrx-2 interactions using specific inhibitors may result in a dysfunctional parasite translocon that is rendered unable to secrete pathogenic proteins into hosts. This approach therefore offers a new focus for anti-malarial drug development.

Crystal structure and solution characterization of the thioredoxin-2 from Plasmodium falciparum, a constituent of an essential parasitic protein export complex

“…The 2.9 Å resolution structure of Plasmodium TRX2 reported previously [23] (PDB: 3UL3) shows that the 16 extra N-terminal residues (backbone only for residues R54 through K69) can adopt an extended featureless conformation (Fig. 3A and Supplementary Fig.…”

“…Secondary structure elements correspond to our structure. Residues T24-K69 (shaded in yellow) are not seen in our structure, residues R54-K69 (shaded in blue) were observed in a previously published structure [23]. (B) Crystal structure of TRX2 from Plasmodium falciparum .…”

“…In the leishmanial trypanothione reductase [35] and the schistosomal thioredoxin–glutatione reductase [36], gold binds to and bridges the two active-site cysteine residues that are 3.5–4.5 Å apart. Auro-thiomalate also inhibits Plasmodium TRX2 [23]; the strongly thiophilic gold atom is likely to interact with the two SH groups of the C 82 XXC 85 catalytic motif of TRX2 in a similar way.…”

“…Attempts to fit experimental data against the theoretical scattering curve calculated from our crystal structure result in a poor fit (χ 2 = 2.347) indicating a significant deviation between our model and the average conformation in solution. However, we also fitted our data using the monomer and the pseudo-dimer models of TRX2 described in the previously reported crystal structure [23] (PDB 3UL3) (Supplementary Figs. S3 and S4) where the refined model is longer by 16 amino acids at its N-terminus.…”

“…Small-molecule inhibitors of thioredoxins and ClpB AAA + proteins have been described and identified using high-throughput screening [22] and/or computational methods [23]. To this aim, we have characterized the solution and crystal structures of P. falciparum TRX2 to facilitate the rational design of inhibitors and gain mechanistic insights into the molecular mechanism of this essential parasitic protein export machine.…”