Antimicrobial Properties and Mode of Action of the Pyrrothine Holomycin

Abstract

Holomycin, a member of the pyrrothine class of antibiotics, displayed broad-spectrum antibacterial activity, inhibiting a variety of gram-positive and gram-negative bacteria, with the exception of Enterobacter cloacae, Morganella morganii, and Pseudomonas aeruginosa. The antibiotic lacked activity against the eukaryotic microorganisms Saccharomyces cerevisiae and Candida kefyr. Holomycin exhibited a bacteriostatic response against Escherichia coli that was associated with rapid inhibition of RNA synthesis in whole cells. Inhibition of RNA synthesis could have been a secondary consequence of inhibiting tRNA aminoacylation, thereby inducing the stringent response. However, the levels of inhibition of RNA synthesis by holomycin were similar in a stringent and relaxed pair of E. coli strains that were isogenic except for the deletion of the relA gene. This suggests that inhibition of RNA synthesis by holomycin could reflect direct inhibition of DNA-dependent RNA polymerase. Examination of the effects of holomycin on the kinetics of the appearance of ␤-galactosidase in induced E. coli cells was also consistent with inhibition of RNA polymerase at the level of RNA chain elongation. However, holomycin only weakly inhibited E. coli RNA polymerase in assays using synthetic poly(dA-dT) and plasmid templates. Furthermore, inhibition of RNA polymerase was observed only at holomycin concentrations in excess of those required to inhibit the growth of E. coli. It is possible that holomycin is a prodrug, requiring conversion in the cell to an active species that inhibits RNA polymerase.Thiolutin and holomycin (see Fig. 1) are members of the pyrrothine class of naturally occurring antibiotics that are characterized by the possession of a unique pyrrolinonodithiole nucleus (2). Although these antimicrobial agents were originally discovered more than 40 years ago (6, 13, 23, 26), relatively little is known about their mode of action. Limited studies with thiolutin suggest that the pyrrothines may act as inhibitors of DNA-dependent RNA polymerase. Thus, thiolutin preferentially inhibits RNA synthesis in both Saccharomyces cerevisiae (10) and Escherichia coli (14) and is reported to be a potent inhibitor of partially purified RNA polymerases from S. cerevisiae (10, 25). Furthermore, by monitoring the effects of thiolutin on the induction of ␤-galactosidase in E. coli, Khachatourians and Tipper (14) concluded that the antibiotic interfered with RNA chain elongation rather than with initiation of transcription.However, there are several observations that cast doubt upon the hypothesis that thiolutin, and therefore the pyrrothines as a class, prevents microbial growth by interfering with the elongation of RNA transcripts catalyzed by RNA polymerase. For instance, Sivasubramanian and Jayaraman (24) were unable to reproduce the observations made by Khachatourians and Tipper (14) concerning the effects of thiolutin on ␤-galactosidase induction in E. coli. Thus, these authors (24) concluded that thiolutin inhibits initiation of RNA tran...

Synthesis of Dithiolopyrrolone Derivatives and Their Leukocyte-Increasing Activities

“…These results suggest that introduction of 2,4-dimethoxyphenyl group to N-4 position is favorable. For R 3 R 2 N compounds, ethylamino group and diethylamino group were better for the activity, on the other hand, corresponding methylamino, bis (2-hydroethyl)amino, pyrrolyl, piperidyl, 2-hydroxyethylamino analogs (4,7,8,9,10) showed weak leukocyte-increasing activity, and the other heterocyclic derivatives (11, 12, 13) also did not display obvious leukocyte-increasing activity.…”

“…[8][9][10][11][12][13][14] Dithiolopyrrolones have also been reported to have anticancer activity, [15][16][17] and shown potent membrane stabilization and platelet anti-aggregate activities. 18 We first reported that ZL-004 ( Figure 1) exhibited antileukopenia activity.…”

Bacterial Transcription as a Target for Antibacterial Drug Development

“…Both compounds demonstrated broad activity against bacterial and fungal RNAPs, and functional analysis showed that that they could inhibit bacterial transcription elongation and yeast transcription initiation (149)(150)(151).…”

“…Thiolutin and holomycin are types of pyrrothine natural products isolated from Streptomyces luteosporeus and Streptomyces clavuligerus, respectively (148,149). Both compounds demonstrated broad activity against bacterial and fungal RNAPs, and functional analysis showed that that they could inhibit bacterial transcription elongation and yeast transcription initiation (149)(150)(151).…”

Novel Hybrid-Type Antimicrobial Agents Targeting the Switch Region of Bacterial RNA Polymerase

“…11,12 In addition, 4 showed the inhibition of RNA synthesis, 11 and the calculate log P (ClogP) did not exceed 2.0. 13 These properties fascinated us to hybridize myxopyronins with the holothin molecule to expect the efficacy beyond our anticipations.…”