Inhibitory compounds targeting Plasmodium falciparum Gyrase B

Malaria persists as a major health problem due to the spread of drug resistance and the lack of effective vaccines. DNA gyrase is a well-validated and extremely effective therapeutic target in bacteria, and it is also known to be present in the apicoplast of malarial species including Plasmodium falciparum . This raises the possibility that it could be a useful target for novel antimalarials. To date, characterisation and screening of this gyrase has been hampered by difficulties in cloning and purification of the GyrA subunit, which is necessary together with GyrB for reconstitution of the holoenzyme. To overcome this, we employed a library of compounds with specificity for P. falciparum GyrB and assessed them in activity tests utilising P. falciparum GyrB together with E. coli GyrA to reconstitute a functional hybrid enzyme. Two inhibitory compounds were identified that preferentially inhibited the supercoiling activity of the hybrid enzyme over the E. coli enzyme. Of these, purpurogallin (PPG) was found to disrupt DNA binding to the hybrid gyrase complex and thus reduce the DNA-induced ATP hydrolysis of the enzyme. Binding studies indicated that PPG showed higher affinity binding to P. falciparum GyrB compared to the E. coli protein. We suggest that PPG achieves its inhibitory effect on gyrase through interaction with P. falciparum GyrB leading to disruption of DNA binding and, consequently reduction of DNA-induced ATPase activity. The compound also showed an inhibitory effect against the malaria parasite in vitro and maybe of interest for further development as an antimalarial agent.

Chiral carbon dots - a functional domain for tyrosinase Cu active site modulation via remote target interaction

Nano-hybrid-enzyme is an ideal catalytic system that integrates various advantages from biocatalysis, nanocatalysis to homogeneous and heterogeneous catalysis. However, great efforts are still needed to fully understand the interactions between...

Unique features of the ketosynthase domain in a nonribosomal peptide synthetase–polyketide synthase hybrid enzyme, tenuazonic acid synthetase 1

Many microbial secondary metabolites are produced by multienzyme complexes comprising nonribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs). The ketosynthase (KS) domains of polyketide synthase normally catalyze the decarboxylative Claisen condensation of acyl and malonyl blocks to extend the polyketide chain. However, the terminal KS domain in tenuazonic acid synthetase 1 (TAS1) from the fungus Pyricularia oryzae conducts substrate cyclization. Here, we report on the unique features of the KS domain in TAS1. We observed that this domain is monomeric, not dimeric as is typical for KSs. Analysis of a 1.68-Å resolution crystal structure suggests that the substrate cyclization is triggered via proton abstraction from the active methylene moiety in the substrate by a catalytic His-322 residue. Additionally, we show that TAS1 KS promiscuously accepts aminoacyl substrates and that this promiscuity can be increased by a single amino acid substitution in the substrate-binding pocket of the enzyme. These findings provide insight into a KS domain that accepts the amino acid–containing substrate in an NRPS–PKS hybrid enzyme and provide hints to the substrate cyclization mechanism performed by the KS domain in the biosynthesis of the mycotoxin tenuazonic acid.

Correction: High yield 5-(hydroxymethyl)furfural production from biomass sugars under facile reaction conditions: a hybrid enzyme- and chemo-catalytic technology

Correction for ‘High yield 5-(hydroxymethyl)furfural production from biomass sugars under facile reaction conditions: a hybrid enzyme- and chemo-catalytic technology’ by Siamak Alipour, Green Chem., 2016, 18, 4990–4998.