Role of lipopolysaccharide in antimicrobial peptide membrane interactions probed by deuterium NMR of whole cells

Sarika Kumari
PhD Student
Department of Biochemistry

Sept. 27, 2021
1-2 p.m.

The direct link for the meeting is: https://mun.webex.com/mun/j.php?MTID=m5b11183abdb96b335d4d68c93ae8be1f 

Abstract:

Antimicrobial Peptides (AMPs) have been studied for more than two decades because they promise to help overcome the problem of resistance to conventional antibiotics. However, AMPs have not been as successful as hoped, perhaps because we lack a detailed understanding of their mechanisms of action. To understand these mechanisms, numerous biophysical techniques, including solid-state ²H NMR, have been used to study membrane disruption both in model lipid systems and in intact bacteria. In the real biological context of AMPs, studies suggest that, in addition to interaction with lipids, it is essential to consider non-lipid components the cell envelopes Gram-negative bacteria have a lipopolysaccharide (LPS) outer membranes component that protects bacteria from AMPs. This study investigated how LPS affects AMP- induced membrane disruption. MSI-78 is an AMP that has been shown to disrupt the lipid membranes of target bacteria. We disrupt the LPS layer of Escherichia coli cells (E. coli) via chelation of the stabilizing divalent cations. However, the ²H NMR spectra of E. coli demonstrated that the EDTA concentrations of 2.5 mM and 9.0 mM do not affect the lipid acyl chain order. Interestingly, we found that the ²H NMR spectra of E. coli with a 9.0 mM concentration of EDTA in the presence of MSI-78 show a slight increase of the lipid acyl chain disorder compared to MSI-78 alone. Thus, our results suggest that disruption of the LPS layer very slightly sensitizes bacteria to membrane disruption by MSI-78.