Structural and functional dissection of aminocoumarin antibiotic biosynthesis: a review David M. Lawson • Clare E. M. Stevenson Received: 26 September 2011 / Accepted: 12 May 2012 / Published online: 27 May 2012 Ó Springer Science+Business Media B.V. 2012 Abstract Aminocoumarin antibiotics are natural products of soil-dwelling bacteria called Streptomycetes. They are potent inhibitors of DNA gyrase, an essential bacterial enzyme and validated drug target, and thus have attracted considerable interest as potential templates for drug devel- opment. To date, aminocoumarins have not seen widespread clinical application on account of their poor pharmacologi- cal properties. Through studying the structures and mecha- nisms of enzymes from their biosynthetic pathways we will be better informed to redesign these compounds through rational pathway engineering. Novobiocin, the simplest compound, requires at least seventeen gene products to convert primary metabolites into the mature antibiotic. We have solved the crystal structures of four diverse biosyn- thetic enzymes from the novobiocin pathway, and used these as three-dimensional frameworks for the interpretation of functional and mechanistic data, and to speculate about how they might have evolved. The structure determinations have ranged from the routine to the challenging, necessitating a variety of different approaches. Keywords Antibiotic biosynthesis Á Enzyme evolution Á Structure determination Á Streptomyces Á X-ray crystallography Abbreviations PDB Protein Data Bank ASU Asymmetric unit NCS Non-crystallographic symmetry SAM S-adenosyl-L-methionine SAH S-adenosyl-L-homocysteine SIRAS Single isomorphous replacement with anomalous scattering Introduction The aminocoumarin class of antibiotics are natural products of Streptomycetes, which are ubiquitous soil-dwelling bac- teria, and the source of the majority of naturally-derived antibiotics in current clinical use [1]. The interest in ami- nocoumarins stems from their ability to inhibit DNA gyrase [2], an essential enzyme in bacteria and a validated drug target [3]. They bind to the B subunit of gyrase and competitively inhibit the ATPase activity of the enzyme [4]. The three classical aminocoumarins, novobiocin (Fig. 1), clorobiocin and coumermycin A 1 , are biosynthesised by three separate Streptomyces species, and share common structural features, namely an aromatic acyl component (ring A), a 3-amino-4,7-dihydroxycoumarin moiety (ring B) and an L-noviosyl sugar (ring C) [5–8]. A further type of aminocoumarin, termed the simocyclinones, will not be considered here. Despite their potency against DNA gyrase, the amino- coumarins have poor pharmacological properties, display- ing limited solubility in water, low penetration into Gram negative bacteria and moderate toxicity to humans. Nev- ertheless, novobiocin is licensed for the treatment of some Gram positive organisms including methicillin-resistant Staphylococcus aureus [9, 10] and Borrelia burgdorferi [11] (the causative agent of Lyme’s disease), and shows synergistic effects with anti-tumour drugs, such as etopo- side or teniposide [12], through the inhibition of multidrug resistance proteins. DNA topoisomerase IV is an additional D. M. Lawson (&) Á C. E. M. Stevenson Department of Biological Chemistry, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK e-mail: david.lawson@jic.ac.uk 123 J Struct Funct Genomics (2012) 13:125–133 DOI 10.1007/s10969-012-9138-2