310-Helix stabilization and screw sense control via stereochemically configured 4-atom hydrocarbon staples.

The 310-helix is a crucial secondary structure in proteins, playing an essential role in various protein-protein interactions, yet stabilizing it in biologically relevant peptides remains challenging. In this study, we investigated the potential of 4-atom hydrocarbon staples to stabilize 310-helices in peptides. Using ring-closing metathesis, we demonstrated that the staple's configuration is critical for both the stabilization and screw sense control of 310-helices. Circular dichroism spectroscopy revealed that the Ri,i+3S(4) staple-a 4-atom cross-link with (R)-configuration at the i position, (S)-configuration at the i + 3 position, and flanked by methyl groups-strongly induces right-handed 310-helices, especially in sequences with proteinogenic l-amino acids. Furthermore, multiple staples effectively stabilized longer peptides, underscoring the versatility of this approach for applications in peptide therapeutics and biomolecular engineering.

Amine-bearing hydrocarbon cross-links: Tailoring helix stability, hydrophilicity, and synthetic adaptability in peptides.

This study comprehensively explored the helix-stabilizing effects of amine-bearing hydrocarbon cross-links (ABXs), revealing their context-dependent nature influenced by various structural parameters. Notably, we identified a 9-atom ABX as a robust helix stabilizer, showcasing versatile synthetic adaptability while preserving peptide water solubility. Future investigations are imperative to fully exploit this system's potential and enrich our chemical toolkit for designing innovative peptide-based biomolecules.

Lysine-homologue substitution: Impact on antimicrobial activity and proteolytic stability of cationic stapled heptapeptides.

Numerous natural antimicrobial peptides (AMPs) exhibit a cationic amphipathic helical conformation, wherein cationic amino acids, such as lysine and arginine, play pivotal roles in antimicrobial activity by aiding initial attraction to negatively charged bacterial membranes. Expanding on our previous work, which introduced a de novo design of amphipathic helices within cationic heptapeptides using an 'all-hydrocarbon peptide stapling' approach, we investigated the impact of lysine-homologue substitution on helix formation, antimicrobial activity, hemolytic activity, and proteolytic stability of these novel AMPs. Our results demonstrate that substituting lysine with ornithine enhances both the antimicrobial activity and proteolytic stability of the stapled heptapeptide AMP series, while maintaining low hemolytic activity. This finding underscores lysine-homologue substitution as a valuable strategy for optimizing the therapeutic potential of diverse cationic AMPs.

Streptomyces tagetis sp. nov., a chromomycin producing bacteria isolated from the roots of Tagetes patula.

A novel halotolerant actinobacterium, designated as RG38T, capable of producing black extracellular melanin pigment on SP2 agar, was isolated from the roots of Tagetes patula. Comparative analysis of the 16S rRNA gene sequence revealed the highest similarity to Streptomyces collinus NBRC 12759T (99.3%). Phylogenetic analysis showed that strain RG38T clustered within the genus Streptomyces forming a monophyletic cluster with its close relatives. The average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and amino-acid identity (AAI) values between strain RG38T and related species within the genus Streptomyces were below the standard threshold for prokaryotic species delineation. The DNA G + C content of the strain RG38T was determined to be 73.3%. The genome size measured 7,150,598 bp comprising 17 contigs and encompassed 6,053 protein coding genes. AntiSMASH analysis of the whole genome revealed 35 putative biosynthetic gene clusters (BGCs) responsible for various secondary metabolites. Among these clusters, two gene clusters exhibited 100% similarity to the chromomycin A3, albaflavenone, and anthracimycin, respectively. These compounds were reported to possess significant anticancer and antibacterial activities. LC-MS-based analysis, coupled with further isolation studies, confirmed the production of chromomycins A2 (1), A3 (2), and their derivatives, along with their antibiotic activities. These findings underscore the potential of this novel strain as a novel resource for the discovery of diverse antimicrobial compounds. This study is the first to report an antimicrobial compound producing Streptomyces species isolated from medicinal plant T. patula. Based on a polyphasic study, the strain RG38T isolated from an unexplored habitat with a high potential for new natural products represents a novel species within the genus Streptomyces. Accordingly, we propose the name Streptomyces tagetis sp. nov. for this novel species, with the type strain is RG38T (=KCTC 49624T = TBRC 15113T).