RESUMO
In response to the pressing global challenge of antibiotic resistance, time efficient design and synthesis of novel antibiotics are of immense need. Polycyclic polyprenylated acylphloroglucinols (PPAP) were previously reported to effectively combat a range of gram-positive bacteria. Although the exact mode of action is still not clear, we conceptualized a late-stage divergent synthesis approach to expand our natural product-based PPAP library by 30 additional entities to perform SAR studies against methicillin-resistant Staphylococcus aureus (MRSA). Although at this point only data from cellular assays are available and understanding of molecular drug-target interactions are lacking, the experimental data were used to generate 3D-QSAR models via an artificial intelligence training and to identify a common pharmacophore model. The experimentally validated QSAR model enabled the estimation of anti-MRSA activities of a virtual compound library consisting of more than 100.000 in-silico generated B PPAPs, out of which the 20 most promising candidates were synthesized. These novel PPAPs revealed significantly improved cellular activities against MRSA with growth inhibition down to nanomolar concentrations.
RESUMO
In recent years, it became apparent that not only autotrophic but also most other bacteria require CO2 or bicarbonate for growth. Two systems are available for the acquisition of dissolved inorganic carbon supply (DICS): the cytoplasmic localized carbonic anhydrase (CA) and the more recently described bicarbonate transporter MpsAB (membrane potential generating system). In the pathogenic species Staphylococcus aureus, there are contradictions in the literature regarding the presence of a CA or MpsAB. Here, we address these contradictions in detail. We could demonstrate by careful BLASTp analyses with 259 finished and 4,590 unfinished S. aureus genomes that S. aureus does not contain CA and that the bicarbonate transporter MpsAB is the only DICS system in this species. This finding is further supported by two further pieces of evidence: (i) mpsAB deletion mutants in four different S. aureus strains failed to grow under atmospheric air, which should not be the case if they possess CAs, since we have previously shown that both CA and MpsAB can substitute for each other, and (ii) S. aureus is completely resistant to CA inhibitors, whereas Staphylococcus carnosus, which has been shown to have only CA, was inhibited by ethoxyzolamide (EZA). Taken together, we demonstrate beyond doubt that the species S. aureus possesses only the bicarbonate transporter MpsAB as its sole DICS system. IMPORTANCE The discrepancies in the current literature and even in NCBI database, which listed some protein sequences annotated as Staphylococcus aureus carbonic anhydrase (CA), are misleading. One of the existing problems in publicly available sequence databases is the presence of incorrectly annotated genes, especially if they originated from unfinished genomes. Here, we demonstrate that some of these unfinished genomes are of poor quality and should be interpreted with caution. In the present study, we aimed to address these discrepancies and correct the current literature about S. aureus CA, considering the medical relevance of S. aureus. If left unchecked, these misleading studies and wrongly annotated genes might lead to a continual propagation of wrong annotation and, consequently, wrong interpretations and wasted time. In addition, we also show that bicarbonate transporter MpsAB-harboring bacteria are resistant to CA inhibitor, suggesting that pathogens possessing both MpsAB and CA are not treatable with CA inhibitors.