The novel antibiotic rhodomyrtone traps membrane proteins in vesicles with increased fluidity

Abstract

The acylphloroglucinol rhodomyrtone is a promising new antibiotic isolated from the rose myrtle Rhodomyrtus tomentosa, a plant used in Asian traditional medicine. While many studies have demonstrated its antibacterial potential in a variety of clinical applications, very little is known about the mechanism of action of rhodomyrtone. Preceding studies have been focused on intracellular targets, but no specific intracellular protein could be confirmed as main target. Using live cell, high-resolution, and electron microscopy we demonstrate that rhodomyrtone causes large membrane invaginations with a dramatic increase in fluidity, which attract a broad range of membrane proteins. Invaginations then form intracellular vesicles, thereby trapping these proteins. Aberrant protein localization impairs several cellular functions, including the respiratory chain and the ATP synthase complex. Being uncharged and devoid of a particular amphipathic structure, rhodomyrtone did not seem to be a typical membrane-inserting molecule. In fact, molecular dynamics simulations showed that instead of inserting into the bilayer, rhodomyrtone transiently binds to phospholipid head groups and causes distortion of lipid packing, providing explanations for membrane fluidization and induction of membrane curvature. Both its transient binding mode and its ability to form protein-trapping membrane vesicles are unique, making it an attractive new antibiotic candidate with a novel mechanism of action.

A selective membrane-targeting repurposed antibiotic with activity against persistent methicillin-resistant Staphylococcus aureus

“…S9). Consistent with these data, a recent study reported that the antibiotic agent rhodomyrtone causes increased membrane fluidity in Bacillus subtilis and kills its persister cells (23).…”

“…Insertion of particular membrane disrupting compounds into lipid bilayers is known to cause dramatic changes in membrane fluidity that disrupts the normal liquid-crystalline phase of the membrane (21)(22)(23). This results in passive permeabilization, loss of membrane protein functions, leakage of cellular components, and bacterial death (24).…”

Antibacterial mechanism of rhodomyrtone involves the disruption of nucleoid segregation checkpoint in Streptococcus suis

“…This phenomenon could also be applied to rhodomyrtone treatment in S. suis as the dramatic reduction in cell number was seen only after 4 hours at the highest concentration of rhodomyrtone treatment and this duration was extended in dosedependent manners. These might due to the combinatorial effects of rhodomyrtone on nucleoid segregation and loss of function of other proteins trapped in RIF (Saeloh et al 2018). Therefore, the additional functional consequence of rhodomyrtone treatment on other protein which directly or indirectly involved in the nucleoid segregation remains to be elucidated.…”

“…Furthermore, Saeloh et al (2018) demonstrated that rhodomyrtone caused delocalization of membrane proteins correlated to the cell size and shape defects in B. subtilis and S. aureus (Saising et al 2018;Sianglum et al 2018). Two important cell division proteins, DivIVA and FtsA were known to associate with FtsZ during the septum formation as a nal step of cell division.…”

“…Following the treatment, S. aureus membrane potential decrease immediately at low doses resulted in releasing of ATP and cytoplasmic protein without pore-formation effect (Saising et al 2018). Other workers demonstrated the increase in membrane uidity and the collapsed membrane potential in Bacillus subtilis as well as the relocalization of seven membrane proteins (FtsA, DivIVA, MinD, PlsX, MreB, MurG and SdhA), trapping within the region of increased lipid uidity (RIF) (Saeloh et al 2018). Accumulation of high concentration of FtsA and other divisome proteins suggested that they might interfere with the dynamics of cell division complex that need to position at the midcell area in timely and orderly manner.…”