MRI, protein engineering, genetically encoded reporters, California

Molecular Engineering for Deep Tissue Imaging

Many areas of biomedical research demand technologies that allow for the observation of specific cell states, fates, and functions within intact organisms. Magnetic resonance imaging (MRI) is a perfect tool for this purpose since it can noninvasively capture large tissue volumes with high spatial resolution and anatomical detail. However, visualizing cellular functions using MRI necessitates molecular tools that connect biological events to changes in MRI contrast. To tackle this critical, unmet biomedical need, our research program combines imaging science with synthetic biology, protein engineering, and chemical biology. Our two primary areas of research are briefly summarized below.

Genetically Encoded Diffusion-based Reporters for MRI
In 2016, we led the development of a new molecular reporter for MRI based on aquaporins, a class of channel proteins that facilitates water exchange across cell membranes. Unlike normal cells, where plasma membranes restrict water diffusion, cells engineered to express aquaporins allow for free water exchange, resulting in increased water diffusivity that can be visualized using diffusion-weighted imaging, a widely used MRI technique. By using aquaporins as a starting point and integrating synthetic biology, diffusion biophysics, protein engineering, and chemical biology, we aim to discover new (and often unorthodox) solutions to the grand challenges of creating specific, sensitive, and biologically responsive MRI reporters.

Genetically Encoded Flavin-binding Reporters for Optical Imaging
In a parallel thrust, we aim to address the drawback of GFP-derived reporters, which require oxygen for light emission. This constraint restricts their usefulness in low-O2 conditions, which are crucial for studying biological systems in hypoxia, such as in vitro models of the tumor microenvironment and GI tract. To address this issue, we develop fully autonomous (i.e., dye-free) O2-independent fluorescent reporters by engineering a class of flavin-binding photoreceptors known as light-oxygen-voltage (LOV) sensing proteins.