Steve Ealick's Research Group
Soriano EV, Zhang Y, Colabroy K, Sanders JM, Settembre EC, Dorrestein PC, Begley TP, and Ealick SE. Active Site Models for Complexes of Quinolinate Synthase with Substrates and Intermediates. Acta Crystallogr. D. 69:1685–1696 (2013).
Quinolinate synthase (QS) catalyzes the condensation of iminoaspartate and dihydroxyacetone phosphate to form quinolinate, the universal precursor for the de novo biosynthesis of nicotinamide adenine dinucleotide. QS has been difficult to characterize due either to instability or lack of activity when it is overexpressed and purified. We have determined the structure of QS from Pyrococcus furiosus at 2.8 Å resolution. The structure is a homodimer consisting of three domains per protomer. Each domain shows the same topology with a four-stranded parallel β-sheet flanked by four α-helices, suggesting that the domains are the result of gene triplication. Biochemical studies of QS indicate the enzyme requires a [4Fe-4S] cluster, which is lacking in our crystal structure, for full activity. The organization of domains in the protomer is distinctly different from that of a monomeric structure of QS from Pyrococcus horikoshii (Sakuraba, H, et al., J. Biol. Chem. 280, 26645-26648, 2005). The domain arrangement in P. furiosus QS may be related to protection of cysteine side chains, which are required to chelate the [4Fe-4S] cluster, prior to cluster assembly.
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