Novobiocin, also known as albamycin or cathomycin, is an aminocoumarin antibiotic that is produced by the actinomycete Streptomyces niveus, which has recently been identified as a subjective synonym for S. spheroides a member of the class Actinomycetia. Other aminocoumarin antibiotics include clorobiocin and coumermycin A1. Novobiocin was first reported in the mid-1950s (then called streptonivicin). Clinical use It is active against Staphylococcus epidermidis and may be used to differentiate it from the other coagulase-negative Staphylococcus saprophyticus, which is resistant to novobiocin, in culture. Novobiocin was licensed for clinical use under the tradename Albamycin (Upjohn) in the 1960s. Its efficacy has been demonstrated in preclinical and clinical trials. The oral form of the drug has since been withdrawn from the market due to lack of efficacy. A combination product of novobiocin and tetracycline, sold by Upjohn under brand names such as Panalba and Albamycin-T, was in particular the subject of intense FDA scrutiny before it was finally taken off the market. Novobiocin is an effective antistaphylococcal agent used in the treatment of MRSA. Mechanism of action The molecular basis of action of novobiocin, and other related drugs clorobiocin and coumermycin A1 has been examined. Aminocoumarins are very potent inhibitors of bacterial DNA gyrase and work by targeting the GyrB subunit of the enzyme involved in energy transduction. Novobiocin as well as the other aminocoumarin antibiotics act as competitive inhibitors of the ATPase reaction catalysed by GyrB. The potency of novobiocin is considerably higher than that of the fluoroquinolones that also target DNA gyrase, but at a different site on the enzyme. The GyrA subunit is involved in the DNA nicking and ligation activity. Novobiocin has been shown to weakly inhibit the C-terminus of the eukaryotic Hsp90 protein (high micromolar IC50). Modification of the novobiocin scaffold has led to more selective Hsp90 inhibitors. Novobiocin has also been shown to bind and activate the Gram-negative lipopolysaccharide transporter LptBFGC. The ATP binding pocket of polymerase theta is blocked by novobiocin resulting in a loss of ATPase activity. This results in the loss of microhomology-mediated end joining as a pathway for homologous recombination deficient cells to circumvent DNA damaging agents. The action of novobiocin is syngeristic with PARP inhibitors for reducing tumor size in a mouse model. Structure Novobiocin is an aminocoumarin. Novobiocin may be divided up into three entities; a benzoic acid derivative, a coumarin residue, and the sugar novobiose. X-ray crystallographic studies have