Abstract
Differential Scanning Calorimetry (DSC) of intact Escherichia coli (E. coli) was used to identify non-lipidic targets of the antimicrobial peptide (AMP) MSI-78. The DSC thermograms revealed that, in addition to its known lytic properties, MSI-78 also has a striking effect on ribosomes. MSI-78’s effect on DSC scans of bacteria was similar to that of kanamycin, an antibiotic drug known to target the 30S small ribosomal subunit. An in vitro transcription/translation assay helped confirm MSI-78’s targeting of ribosomes. The scrambled version of MSI-78 also affected the ribosome peak of the DSC scans, but required greater amounts of peptide to cause a similar effect to the unscrambled peptide. Furthermore, the effect of the scrambled peptide was not specific to the ribosomes; other regions of the DSC thermogram were also affected. These results suggest that MSI-78’s effects on E. coli are at least somewhat dependent on its particular structural features, rather than a sole function of its overall charge and hydrophobicity. When considered along with earlier work detailing MSI-78’s membrane lytic properties, it appears that MSI-78 operates via a multi-hit mechanism with multiple targets.
Highlights
antimicrobial peptide (AMP) are a crucial component of the innate immune system of many organisms and can protect against a variety of invading pathogens including bacteria, viruses, and microbial eukaryotes (Shai, 1999; Zasloff, 2002; Jenssen, Hamill & Hancock, 2006; Nguyen, Haney & Vogel, 2011; Wimley & Hristova, 2011; Bechinger & Salnikov, 2012)
We describe differential scanning calorimetry (DSC) studies of the AMP MSI-78 interacting with whole bacteria
Differential scanning calorimetry was used to assess the thermal transitions in whole E. coli JM109 cells upon addition of increasing concentrations of MSI-78 and small molecule antibiotics
Summary
AMPs are a crucial component of the innate immune system of many organisms and can protect against a variety of invading pathogens including bacteria, viruses, and microbial eukaryotes (Shai, 1999; Zasloff, 2002; Jenssen, Hamill & Hancock, 2006; Nguyen, Haney & Vogel, 2011; Wimley & Hristova, 2011; Bechinger & Salnikov, 2012). AMPs have been isolated from a plethora of organisms, including plants, humans, frogs, and bacterial species. They are generally short, typically ranging from 12 to 50 amino acids in length, cationic, due to an abundance of basic residues (lysine, arginine, histidine), and amphipathic, with some AMPs displaying a hydrophobicity of >50%. By focusing solely on the lipids, studies that are limited to model membrane systems fail to capture the myriad of potentially important interactions that AMPs may have with their target microbes
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