Rediscovery of known antibiotics from actinobacteria, especially Streptomyces, has become a bottleneck issue. Nowadays, more specific identification and dereplication could be acquired by a combination of modern analytic techniques with various databases. In this study, 261 actinobacterial strains were isolated from 8 mangrove soil samples by culture-dependent method. A total of 83 strains were selected to evaluate antibacterial activities and mechanisms by disc diffusion method and a unique double fluorescent protein reporter system (pDualrep2), respectively. Thirty-two strains exhibited antagonistic activity against at least one of the “ESKAPE” pathogens. Four Streptomyces strains (B475, B486, B353, and B98) showed strong inhibitory activity against Gram-positive bacteria and induced DNA damage SOS response. One Micromonospora strain (B704) exhibited inhibitory activity against several pathogens and induced attenuation-based translational inhibitors reporter. Seven members of quinoxaline-type antibiotics including quinomycin A, quinomycin monosulfoxide, and other five putative new analogues were found from the culture broth of strain B475 by a combination of anti-MRSA guide, HPTLC, HPLC-UV, and UPLC-UV-HRESIMS/MS analysis, Chemspider searching, and MS/MS-based molecular networking analysis. In conclusion, this study not only demonstrated that mangrove is a rich source of actinobacteria with the potentially new antibiotics but showed rapid dereplication of known antibiotics in the early stage can improve efficiency for the discovery of new antibiotics.

Objectives: Aminoglycosides are one of the first classes of natural antibiotics which have not lost relevance due to their broad spectrum of action against Gram-positive, Gram-negative bacteria and mycobacteria. The high growth rate of antimicrobial resistance (AMR) together with the severe side effects of aminoglycosides increase the importance of developing improved semisynthetic derivatives. Methods: In this work, we proposed a synthetic route to new tobramycin derivatives modified at the 6″-position with aminoalkylamine or guanidinoalkylamine residues. Results: The antibacterial activity of the new compounds against reference strains of microorganisms was comparable to the parental tobramycin. In striking contrast to tobramycin (resistance index, >256), its 6″-modified derivatives were significantly more potent against resistant clinical isolates of P. aeruginosa strains (resistance index = 4–16) and they demonstrated a promising AMR circumvention in E. coli strains associated with mutations in the fusA gene encoding elongation factor G. All the obtained tobramycin derivatives exhibited reduced cytotoxicity for the eukaryotic HEK293T cells compared to the tobramycin and thereby they potentially may have improved therapeutic index. The proposed modification of the 6″-position of tobramycin does not change the mechanism of aminoglycoside’s antibacterial activity: new compounds induced translation errors which resulted in the inhibition of protein synthesis in bacterial cells. Conclusions: Taken together, we can suggest that further modifications of the 6″-position of tobramycin may be beneficial for circumvention of AMR to aminoglycosides or used for conjugation with other molecules of interest.

Gene expression is a complex process regulated at multiple levels in eukaryotic cells. Translation frequently represents a pivotal step in the control of gene expression. Among the stages of translation, initiation is particularly important, as it governs ribosome recruitment and the efficiency of protein synthesis. The 5′ untranslated region (5′ UTR) of mRNA plays a key role in this process, often exhibiting a complicated and structured landscape. Numerous eukaryotic mRNAs possess long 5′ UTRs that contain diverse regulatory elements, including RNA secondary structures, specific nucleotide motifs, and chemical modifications. These structural features can independently modulate translation through their intrinsic properties or by serving as platforms for trans-acting factors such as RNA-binding proteins. The dynamic nature of 5′ UTR elements allows cells to fine-tune translation in response to environmental and cellular signals. Understanding these mechanisms is not only fundamental to molecular biology but also holds significant biomedical potential. Insights into 5′ UTR-mediated regulation could drive advancements in synthetic biology and mRNA-based targeted therapies. This review outlines the current knowledge of the structural elements of the 5′ UTR, the interplay between them, and their combined functional impact on translation.

Aminoglycosides are one of the first classes of antibiotics to have been used clinically, and they are still being used today. They have a broad spectrum of antimicrobial activity, making them effective against many different types of bacteria. Despite their long history of use, aminoglycosides are still considered promising scaffolds for the development of new antibacterial agents, particularly as bacteria continue to develop resistances to existing antibiotics. We have synthesized a series of 6″-deoxykanamycin A analogues with additional protonatable groups (amino-, guanidino or pyridinium) and tested their biological activities. For the first time we have demonstrated the ability of the tetra-N-protected-6″-O-(2,4,6-triisopropylbenzenesulfonyl)kanamycin A to interact with a weak nucleophile, pyridine, resulting in the formation of the corresponding pyridinium derivative. Introducing small diamino-substituents at the 6″-position of kanamycin A did not significantly alter the antibacterial activity of the parent antibiotic, but further modification by acylation resulted in a complete loss of the antibacterial activity. However, introducing a guanidine residue led to a compound with improved activity against S. aureus. Moreover, most of the obtained 6″-modified kanamycin A derivatives were less influenced by the resistant mechanism associated with mutations of the elongation factor G than the parent kanamycin A. This suggests that modifying the 6″-position of kanamycin A with protonatable groups is a promising direction for the further development of new antibacterial agents with reduced resistances.

Antimicrobial peptides (AMPs) have recently attracted attention as promising antibacterial agents capable of acting against resistant bacterial strains. In this work, an approach was applied, consisting of the conjugation of a peptide related to the sequences of bactenecin 7 (Bac7) and oncocin (Onc112) with the alkyl(triphenyl)phosphonium (alkyl-TPP) fragment in order to improve the properties of the AMP and introduce new ones, expand the spectrum of antimicrobial activity, and reduce the inhibitory effect on the eukaryotic translation process. Triphenylphosphonium (TPP) derivatives of a decapeptide RRIRPRPPYL were synthesized. It was comprehensively studied how the modification of the AMP affected the properties of the new compounds. It was shown that while the reduction in the Bac7 length to 10 a.a. residues dramatically decreased the affinity to bacterial ribosomes, the modification of the peptide with alkyl-TPP moieties led to an increase in the affinity. New analogs with structures that combined a decapeptide related to Bac7 and Onc112—Bac(1–10, R/Y)—and TPP attached to the C-terminal amino acid residue via alkylamide linkers, inhibited translation in vitro and were found to be more selective inhibitors of bacterial translation compared with eukaryotic translation than Onc112 and Bac7. The TPP analogs of the decapeptide related to Bac7 and Onc112 suppressed the growth of both Gram-negative bacteria, similar to Onc112 and Bac7, and Gram-positive ones, similar to alkyl-TPP derivatives, and also acted against some resistant laboratory strains. Bac(1–10, R/Y)-C2-TPP, containing a short alkylamide linker between the decapeptide and TPP, was transferred into the E. coli cells via the SbmA transporter protein. TPP derivatives of the decapeptide Bac(1–10, R/Y) containing either a decylamide or ethylamide linker caused B. subtilis membrane depolarization, similar to alkyl-TPP. The Bac(1–10, R/Y)-C2-TPP analog was proven to be non-toxic for mammalian cells using the MTT test.

Triphenylphosphonium (TPP) derivatives of a decapeptide related to sequences of bactenecin 7 (Bac7) and oncocin (Onc112) were synthesized and studied as potential antimicrobial compounds using various biochemical and microbiological assays. It was shown that while the reduction of the Bac7 length to 10 a.a. residues dramatically decreases the affinity to bacterial ribosomes, the modification of peptide with alkyl-TPP moieties leads to an increase in the affinity. New analogs which structure combines a decapeptide related to Bac7 and Onc112 — Bac(1-10, R/Y) — and TPP, attached to the C-terminal amino acid residue through alkylamide linkers, inhibit translation in vitro and are found to be more selective inhibitors of bacterial translation as compared with eukaryotic translation, than Onc112 and Bac7. Triphenylphosphonium analogs of a decapeptide related to Bac7 and Onc112 suppress the growth of both gram-negative bacteria, similar to Onc112 and Bac7, and gram-positive ones as alkyl-TPP derivatives, and also act against some resistant laboratory strains. Bac(1-10, R/Y)-C2-TPP, containing a short alkylamide linker between the decapeptide and TPP, is transferred into the E. coli cells via the SbmA transporter protein. TPP derivatives of the decapeptide Bac(1-10, R/Y) containing either decylamide or ethylamide linker cause B. subtilis membrane depolarization, similar to alkyl-TPP. The Bac(1-10, R/Y)-C2-TPP analog is proved to be non-toxic for mammalian cells by MTT-test.