Raquel L. Lieberman, Shannon E. Hill, Rebecca K. Donegan, Elaine Nguyen, Michelle Y. Kwon, Athena Patterson-Orazem, Dustin J.E. Huard
Georgia Institute of Technology
Myocilin is expressed at relatively high levels in trabecular meshwork, and missense mutations in myocilin are linked to the hereditary form of open angle glaucoma. To lay the molecular foundation from which to generate new hypotheses regarding myocilin function and disease involvement, our lab has taken a divide-and-conquer structural approach. Using biochemical and biophysical methods, we have assembled a picture of full-length myocilin, including its supramolecular arrangement as defined by its coiled coil and olfactomedin protein domains. The N-terminal coiled coil region imparts an unprecedented tripartite configuration, which affects the clustering and spacing of C-terminal olfactomedin domains. Annotated glaucoma-causing variants within each structural domain display vastly different protein defects. The olfactomedin domain is exquisitely sensitive to mutation. Most olfactomedin-resident mutations are destabilizing and promote templated amyloid-like aggregation; thus far, we have identified just one non-pathogenic mutation that paradoxically stabilizes the protein in a partially folded state. By contrast, the coiled coil domain tolerates mutations without compromising stability or causing aggregation, but selected variants alter the apparent quaternary structure. Taken together, our work broadens the scope of protein misfolding in the pathogenesis of myocilin-associated glaucoma and provides a 3-dimensional picture to stimulate novel structure-based functional hypotheses.