Antimicrobial peptide gramicidin S is accumulated in granules of producer cells for storage of bacterial phosphagens

Abstract

Many antimicrobial peptides are synthesized non-ribosomally in bacteria, but little is known about their subcellular route of biosynthesis, their mode of intracellular accumulation, or their role in the physiology of the producer cells. Here, we present a comprehensive view on the biosynthesis of gramicidin S (GS) in Aneurinibacillus migulanus, having observed a peripheral membrane localization of its synthetases. The peptide gets accumulated in nano-globules, which mature by fusion into larger granules and end up within vacuolar structures. These granules serve as energy storage devices, as they contain GS molecules that are non-covalently attached to alkyl phosphates and protect them from dephosphorylation and premature release of energy. This finding of a fundamentally new type of high-energy phosphate storage mechanism can explain the curious role of GS biosynthesis in the physiology of the bacterial producer cells. The unknown role of the GrsT protein, which is part of the non-ribosomal GS synthetase operon, can thus be assumed to be responsible for the biosynthesis of alkyl phosphates. GS binding to alkyl phosphates may suggest its general affinity to phosphagens such as ATP and GTP, which can represent the important intracellular targets in pathogenic bacteria.

Supreme activity of gramicidin S against resistant, persistent and biofilm cells of staphylococci and enterococci

“…This intrinsic cell-uptake activity has already been explored in eukaryotic cells to specifically target mitochondria with GS derivatives 64 . In the context of prokaryotic cells, together with the ability to bind certain nucleotides and small phosphorylated molecules 29–33 , GS thus seems to be capable of effectively inhibiting bacterial stress response and biofilm development in a fashion previously attributed to IDR. The periplasmic and intracellular binding of anionic phosphorylated metabolites by GS should deplete their levels, and therefore inhibit metabolic activity and possibly even affect gene regulation, e.g., due to interference with phosphorylation in signal transduction processes.…”

“…Citrate phosphate dextrose-stabilized human erythrocyte suspensions were obtained from Karlsruhe Municipal Hospital. The washed 0.25% suspension of erythrocytes were incubated with peptides at 37 °C for 30 min as described earlier 33 . The mixture was pelleted (13 000 rpm, 10 min, 4 °C), and the absorbance of the supernatant was recorded at 540 nm vs. reaction buffer.…”

Simplified Head-to-Tail Cyclic Polypeptides as Biomaterial-Associated Antimicrobials with Endotoxin Neutralizing and Anti-Inflammatory Capabilities

“…The high cytotoxicity of peptide-based biomaterials towards mammalian cells is a major limitation for the development of AMPs as therapeutics. GS not only has great antimicrobial activity, but it is also highly toxic towards mammalian cells, which is attributed to its amphiphilic structure that causes it to lack selectively in its affinity for cellular membranes [35]. In this study, OIR3, IR3 and DIR3, which each have three IR repeating units, demonstrated no hemolytic activity towards erythrocytes (Table 1) and only weak toxicity towards RAW264.7 cells (Figure 2B), while GS had high toxicity towards mammalian cells, similar to that found previously, suggesting that the simplified, engineered active peptides had a great selectivity for negatively charged bacterial membranes versus zwitterionic mammalian cell membranes.…”

Antimicrobial compounds of the genus Bacillus: A review

“…Also, gramicidin S, a small cyclic peptide, synthesized by Bacillus brevis, is an important and powerful antibiotic, effective against a variety of Gram-positive and Gram-negative bacteria (M. BERDITSCH & al [45]; J.W. LIOU & al [46]).…”