X. He et al., Development of a scintillation proximity assay for beta-ketoacyl-acyl carrier protein synthase III, ANALYT BIOC, 282(1), 2000, pp. 107-114
Assays of beta-ketoacyl-acyl carrier protein synthases III (KASIII; FabH),
a key enzyme initiating bacterial type II fatty acid biosynthesis, usually
involve incubation of radiolabeled acetyl-coenzyme A and malonylacyl carrie
r protein (MACP). The radiolabeled acetoacetyl-ACP product is precipitated
and separated from the substrate before quantitation. We have developed a s
cintillation proximity assay (SPA) where use of biotinylated MACP (BMACP) a
llows the generation of a biotinylated acetoacetyl-ACP, This product, when
captured by the streptavidin-coated scintillant-impregnated microspheres, g
enerates an SPA signal. A BMACP K-m of 7.1 mu M was determined using this S
PA with the Streptomyces glaucescens FabH. A similar MACP K-m (6 mu M) was
determined in a precipitation assay, demonstrating that BMACP is an effecti
ve substrate for FabH. IC50 values of 15.2 mu M (SPA) and 24.8 mu M were ob
tained with iodoacetamide and the S. glaucescens FabH, Comparable IC50 valu
es of 160 mu M (SPA) and 125 mu M were also obtained with the antibiotic th
iolactomycin and the Escherichia coli FabH. These observations demonstrate
that FabH inhibitors can be readily detected using a SPA with BMACP and tha
t the effectiveness of inhibitors in the SPA is comparable to that obtained
using MACP and a standard TCA precipitation assay. A FabH SPA adaptable to
high-throughput screening should facilitate the discovery of potential nov
el antibiotics. (C) 2000 Academic Press.