Isolation, characterization, interaction of a thiazolekinase (Plasmodium falciparum) with silver nanoparticles

Malaria, a mosquito-borne infectious disease, is caused by the Plasmodium genus, and remains one of the greatest health challenges worldwide. The malarial parasite possess a biosynthetic pathway for the B-group vitamin incorporating the thiamine metabolizing enzymes; humans on the other hand cannot synthesize the vitamin and require it from within their diet. The vitamin B1 biosynthetic enzyme 5-(2-hydroxyethyl)-4-methylthioazolekinase [EC. 2.7.1.50] from Plasmodium (PfThzK) is particularly attractive as a biomedical target since any inhibition of this enzyme may lead to an effective treatment for malaria. In the present study, PfThzK was recombinantly produced as a 6× His fusion protein in Escherichia coli BL21(DE3) and purified using nickel affinity and size exclusion chromatography. The enzyme was monomeric with a molecular mass of 34 kDa, a specific activity of 295.04 nmol min−1 mg−1 and showed an optimum temperature and pH of 37 °C and 7.5, respectively. The purified PfThzK was non-competitively inhibited (79%) by silver nanoparticles (2-6 nm); Ki = 6.45 μM. A mechanism is suggested for the interaction of the silver nanoparticle with PfThzK through two sulphur bearing amino acids (Met1, Cys206) on the surface of each subunit of the enzyme.