Polymyxin B Identified as an Inhibitor of Alternative NADH Dehydrogenase and Malate: Quinone Oxidoreductase from the Gram-positive Bacterium Mycobacterium smegmatis

Abstract

Tuberculosis is the leading cause of death due to a single infectious agent in the world and the emergence of multidrug-resistant strains prompted us to develop new drugs with novel targets and mechanism. Here, we screened a natural antibiotics library with Mycobacterium smegmatis membrane-bound dehydrogenases and identified polymyxin B (cationic decapeptide) and nanaomycin A (naphtoquinone derivative) as inhibitors of alternative NADH dehydrogenase [50% inhibitory concentration (IC(50)) values of 1.6 and 31 microg/ml, respectively] and malate: quinone oxidoreductase (IC(50) values of 4.2 and 49 microg/ml, respectively). Kinetic analysis on inhibition by polymyxin B showed that the primary site of action was the quinone-binding site. Because of the similarity in K(m) value for ubiquinone-1 and inhibitor sensitivity, we examined amino acid sequences of actinobacterial enzymes and found possible binding sites for L-malate and quinones. Proposed mechanisms of polymyxin B and nanaomycin A for the bacteriocidal activity were the destruction of bacterial membranes and production of reactive oxygen species, respectively, while this study revealed their inhibitory activity on bacterial membrane-bound dehydrogenases. Screening of the library with bacterial respiratory enzymes resulted in unprecedented findings, so we are hoping that continuing efforts could identify lead compounds for new drugs targeting to mycobacterial respiratory enzymes.

Rapid Killing of Acinetobacter baumannii by Polymyxins Is Mediated by a Hydroxyl Radical Death Pathway

“…In fact, Vibrio cholerae treated with polymyxin B exhibits an increase in the transcriptional levels of rpoE, the sigma factor involved in envelope and oxidative stress responses (37). Interestingly, previous studies have indicated that polymyxin B treatment can induce aberrant oxidative respiration (31,40,42). In organisms with no experimentally identified CpxAR envelope stress-sensing two-component system, such as A. baumannii and F. novicida, this envelope stress response may be triggered by other, as-yet-unidentified, sensory systems.…”

Gramicidin S and polymyxins: the revival of cationic cyclic peptide antibiotics

“…In order to identify new inhibitors for alternative respiratory enzymes (i.e., enzymes that are not present in human mitochondria), we screened the Kitasato Institute for Life Sciences Chemical Library [30] with the following enzymes: cytochrome bd quinol oxidase from Escherichia coli [31, 32], bacterial cyanide-insensitive oxidase (CIO, a variant of cytochrome bd) and a single-subunit NADH dehydrogenase (NDH-2) from the acetic acid bacterium Gluconobacter oxydans [33,34], and NDH-2 and malate: quinone oxidoreductase (MQO) from Mycobacterium smegmatis [35] and Pseudomonas aeruginosa [36]. Cytochrome bd and CIO are widely distributed among bacteria and play an important role in microaerophilic respiration and protection against oxygen stress and in the survival and adaptation of pathogenic bacteria [37][38][39].…”

Identification and Validation of Novel Drug Targets for the Treatment of Plasmodium falciparum Malaria: New Insights

“…Plasmodium species possesses a group 2 MQO, in contrast to bacterial group 1 MQO [127]. P. falciparum MQO (PfMQO) is part of both mitochondrial ETC and TCA cycle, substituting other mitochondrial malate dehydrogenases (MDH) [111,112,128].…”