Interaction of Silver Nanoparticles with Triosephosphate Isomerase from Human and Malarial Parasite (Plasmodium falciparum): A Comparative Study.

Recombinant triosephosphate isomerase from Plasmodium falciparum (PfTIM) and humans (hTIM) were expressed, purified and characterised. High specific activity (1207 U x mg(-1)) with a fold purification of -1.8 and a yield of 48% were obtained for hTIM after gel filtration while, in contrast PfTIM afforded a specific activity of 1387 U x mg(-1) with a fold purification of -6.8 and a yield of 57% after gel filtration and prior to dialysis. PfTIM had an optimal pH and temperature, K(m) and V(max) of 5.25, 25 degrees C, 12.8 mM and 1.13 μmol x mL(-1) min(-1) respectively while for hTIM the pH and temperature optima, K(m) and V(max) were 6.75, 30 degrees C; 8.2 mM and 1.35 μmol x ml(-1) min(-1). Polyvinylpyrrolidone stabilised silver nanoparticles (60 nM; 2-6 nm diameter) selectively inhibited PfTIM with a 7-fold decrease in enzyme catalytic efficiency (K(cat)/K(m)) over hTIM. Respective K(i) values were 283 nM [hTIM] and 85.7 nM [PfTIM]. Key structural differences between the two enzyme variants, especially with Cys13 at the dimer interface of PfTIM, were significant enough to suggest unique characteristics allowing for selective targeting of PfTIM by AgNPs.