This is the most recent project in the lab and most of the current students work on a project related to this topic. Lipopeptide antibiotics are a relative new class of antibiotics, of which the best known is daptomycin. Daptomycin is a Ca²⁺-dependent cyclic tridecapeptide, in which the N-terminal amino acid, tryptophan, is amidated with n-decanoic acid. It is a clinically important peptide used in the treatment of multi-drug resistant infections, including those caused by methicillin-resistant S. aureus (MRSA) strains. Daptomycin targets - at least initially - the cytoplasmic membrane of susceptible gram-(+) bacteria, where it leads to lipid clustering. This process requires calcium ions but how Ca²⁺ mediates these initial events is largely unknown. We study peptides and other substances related to daptomycin. The project involves the chemical synthesis of both peptides and organic molecules, a lot of spectroscopy - mainly fluorescence and circular dichroism spectroscopy - calorimetry, and assay development. We collaborate with the lab of Dr. Tom Coombs here at UNCW on this project.

... are amazing! Essentially all living beings have evolved a primary defense mechanism directed at invading or competing organisms. The molecules that constitute these defensive systems are often simple peptides or small proteins that are specific for a particular target organism. For instance, human saliva contains a class of antimicrobial peptides called defensins that help prevent infestation of the oral cavity by yeasts and bacteria. Most antimicrobial and cytolytic peptides act primarily on the cell membrane without the involvement of specific cell surface receptors.

Originally, we set out to study antimicrobial peptides as model systems. Model systems are important because they reveal the general behavior of a class of substances. In this case, we set out to study the principles that govern the movement of peptides and small proteins across cell membranes, which is an important biological phenomenon. As is often the case in research, this straight-forward quest has turned into at least 20 years worth of more questions.

Bacteria are sneaky. When grown in the presence of human serum, they take up lipids from their environment and use those to build their cytoplasmic membranes. That is important because it turns out the the lipid composition of the bacterial membrane determines how sensitive - or insensitive - they are to antibacterial agents, such as antimicrobial peptides.

We built a Langmuir trough! Langmuir troughs are used to study phospholipid monolayers at the air-water interface. Pulmonary surfactant, for instance, is a lipid monolayer formed from a mixture of phospholipids and proteins that coats the inside of alveoli. Without this coating, we would not be able to breathe. Irving Langmuir developed the apparatus named after him and was awarded the Nobel Prize for Chemistry in 1932 for his work in surface chemistry (but he invented scores of other things, too). He was also an excellent communicator and if you want to see him in action, watch the clip posted below (it's fascinating).

We wanted to study lipid-peptide mixtures at the air-water interface but were too poor to immediately buy a commercial instrument (those cost between $50-100K). A former graduate student of mine, Djuro Raskovic, designed and built the first iteration of this instrument, including the microbalance, from 3D printed parts and metal scraps found at the local hardware store. The trough itself is made from PTFE (teflon) and was milled with the help of Alex Elms, an undergraduate honors student in Paulo Almeida's lab. The microbalance was optimized and a computer interface developed by Scott Gere, an undergraduate honors student in my lab, and a chemistry-computer science double major.

After Scott's latest improvements, the instrument is functional and produces quality compression isotherms, of which we are immensely proud. I'm especially proud of the students who designed and built this instrument.