A promising class of potential new antibiotics are the antimicrobial peptides or their synthetic mimics. Herein we assess the effect of the type of cationic side chain (i.e., guanidino vs. amino groups) on the membrane perturbing mechanism of antimicrobial α-peptide–β-peptoid chimeras. Two separate Langmuir monolayers composed of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylglycerol (DPPG) and lipopolysaccharide Kdo2-lipid A were applied to model the outer membranes of Gram-positive and Gram-negative bacteria, respectively. We report the results of the measurements using an array of techniques, including high-resolution synchrotron surface X-ray scattering, epifluorescence microscopy, and in vitro antimicrobial activity to study the molecular mechanisms of peptidomimetic interaction with bacterial membranes. We found guanidino group-containing chimeras to exhibit greater disruptive activity on DPPG monolayers than the amino group-containing analogues. However, this effect was not observed for lipopolysaccharide monolayers where the difference was negligible. Furthermore, the addition of the nitrobenzoxadiazole fluorophore did not reduce the insertion activity of these antimicrobials into both model membrane systems examined, which may be useful for future cellular localization studies.

AMP toxicity and selectivity are poorly understood due to challenges in measuring polydisperse interactions of AMPs within lipid environments. Native or noncovalent mass spectrometry (MS) has recently made significant strides in characterizing the stoichiometry of polydisperse protein complexes and lipid interactions. Here, we employ lipoprotein nanodiscs as a membrane mimetic to assemble AMP complexes for native MS. The nanodiscs are ionized under non-denaturing conditions to introduce the entire nanodisc complex with embedded AMP into the mass spectrometer. By precisely measuring the mass of the intact nanodisc complexes, we can measure the oligomeric state of the AMP without disrupting the lipid bilayer. As a positive control, we observed that gramicidin A forms dimers exclusively, although multiple dimers can be inserted into the nanodisc with sufficient concentration. Ongoing work is investigating AMP complexes with unknown stoichiometries, including LL-37, alamethicin, and melittin. We are also exploring the kinetics of complex assembly by monitoring the formation of specific oligomeric species over time. Ultimately, our goal is that these novel measurements of AMP complex assembly and stoichiometry will shed light on the mechanism of their selectivity and toxicity.

Misquamicut is a coastal community located in Westerly, Rhode Island with a high density of structures that is at risk from inundation, wave, and wind damage from large storm events. The area has suffered significant damage from storms in the past such as the Hurricane of 1938, Hurricane Carol in 1954, and most recently, Superstorm Sandy in 2012. This area is also highly susceptible to sea level rise (SLR), which is predicted to be as high as 7 feet by the year 2100 (NOAA, 2017). A tool called the Coastal Environmental Risk Index (CERI) was used to estimate damage to structures located in Misquamicut due to a 100 year storm event with and without 7 feet of sea level rise. Using CERI, four mitigation strategies were evaluated to improve resiliency of the community: basement window plugs, dune restoration and reinforcement, a tide gate, and elevation of structures.

Antimicrobial peptides (AMPs) are important components of the innate immune system of animals and plants. AMPs are considered promising alternatives to conventional antibiotic treatments, as they exhibit a broad spectrum activity [1]. Understanding the mechanism by which AMPs interact with membranes is fundamental for explaining their biological action. We present a study of two synthetic peptides: Gm1, a cecropine neutral D-like peptide, from Galleria mellonella with activity against Gram-positive, Gram-negative bacteria and fungi [2], and DGm1, a modified structure of Gm1. The aim of the modification was to evaluate the biological activity that increases the cationic amino acids. We have studied the interaction of peptides by applying Fourier-transform infrared spectroscopy (FTIR) and Föster resonance energy transfer spectroscopy (FRET), using pholipid membranes built-up lipopolysaccharide (LPS) and dimyristoylphosphatidylglycerol (DMPG) as representative components of the outer and cytoplasmic bacterial membrane, respectively. Atomic force microscopy (AFM) was used to evaluate the effect of the peptides on the bacterial cells of P. mirabilis R45, and colony counting assay was employed to evaluate the antimicrobial activity. FTIR results showed an opposite effect on the acyl chain packing of lipids. FRET experiments confirmed the incorporation of peptides into the lipid membranes. Considerable alterations were observed in the morphology of P. mirabilis R45. The exposure of the bacteria to Gm1 leads to grooves and when exposed to DGm1, it induces the formation of indentations and cell debris in P. mirabilis R45. The colony counting assay showed that DGm1 also has biological activity. [1] K.L. Brown, R.E. Hancock, Cationic host defense (antimicrobial) peptides,