Biochemical and biophysical characterizations of immunoglobulin superfamily receptors neogenin and L1

Immunoglobulin (Ig) superfamily receptors function in a wide variety of developmental and metabolic processes. We are particularly interested to characterize two Ig superfamily receptors neogenin and L1. The first chapter of the thesis gives a brief review of the biological significance of neogenin and L1 and what has been learned in their functions. In Chapter 2, we described the localization of the hemojuvelin-binding epitope of neogenin to the membrane proximal fifth and sixth fibronectin type III (FNIII) domains, with the sixth FNIII domain contributing the majority of the binding. Chapter 3 presents the crystal structure of this hemojuvelin-binding fragment at 1.8 A, revealing a nearly linear domain arrangement. Hemojuvelin binding sites have been mapped to one face of the sixth FNIII domain based on sequence alignment between neogenin and DCC (Deleted in Colorectal Cancer), a molecule related to neogenin but does not bind to hemojuvelin. These results should also be informative in understanding the interaction between neogenin and repulsive guidance molecule (RGM), the closest homologue of hemojuvelin. The interaction between neogenin and RGM is known to regulate neuronal survival. Chapter 4, the second part of the thesis, describes our studies of L1-mediated homophilic adhesion using biophysical approaches. We built a basis shape model to describe L1-mediated homophilic adhesion between L1-coated giant unilamellar vesicles and flat substrate. Using confocal microscopy techniques, we were able to reconstruct the three-dimensional shape of an adhered vesicle. We developed an algorithm in order to derive adhesion strength from the configurations of adhered vesicles based on our basis shape model using energy minimization approach.