Understanding Highly Heterogeneous Biological Membranes

Biological membranes are highly complex environments that play a central role in a wide range of cellular functions such as cell-cell communication and energy production. Membranes contain hundreds of unique lipids organized on a nanometer length scale, and this organization is critical for cellular function. Membranes contain a large number of lipids, which serve specific functions.

For example, certain lipid species are present as signaling molecules to regulate certain biochemical processes. Abnormal lipid distributions have been linked to human diseases. The specific biological roles of lipid membrane composition are not fully understood since the tools to investigate membrane architectures are severely limited.

Microscopic interactions among the different components, on a molecule-to-molecule basis, determine the microscopic distribution of lipids and local membrane structure. This project will bring forth cutting-edge experimental tools based on time-resolved spectroscopy and single-molecule imaging to investigate the specific environment and the molecular geometries associated with membrane signaling.

In addition, the team will develop multiscale simulation methods to obtain an atomistic view of membranes and aid in the interpretation of experiments. Specifically, the project will focus on understanding how certain negatively-charged lipid species can alter the binding affinities of signaling proteins. This collaborative project will provide a platform for training visiting students across research groups and to increase the number of underrepresented students enrolled in the Chemistry and Neuroscience graduate programs at UT-Austin.

In this project, the research team will investigate lipid membrane environments and the role of signaling lipids using a combination of biochemical methods, fluorescently-labeled lipids, vibrational spectroscopy, single-molecule microscopy, and enhanced-sampling molecular dynamics simulations. Specifically, the team will focus on harvesting intact plasma membranes from mammalian cell lines that will be imaged using fluorescence microscopy and tip-enhanced infrared spectroscopy.

This project seeks to establish a molecular-level view of lipid-lipid and lipid-protein interactions to inform the importance of membrane composition. The following aspects of membranes will be the primary focus of the project: 1. The team will characterize how model transmembrane helices sample a different range of local environments in a mixture with other lipids, with specific emphasis on the sequence of the protein sequence. 2.

The team will determine how proteins become partitioned in heterogeneous bilayers using model helical peptides with a well-defined balance between hydrophobic and hydrophilic residues. The team will measure IR spectra of single transmembrane helices embedded in harvested plasma membranes. 3. The team will explore the role of the membrane as a “signaling lipid reservoir” by capturing the interactions between PIP2 signaling lipids and other anionic lipids within the membrane bulk to inform how these interactions drive signaling functions.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.