The molecular mechanism of cell adhesion by classical cadherins is now understood at an atomic level of detail. However, the basis of desmosomal cadherin function has not yet been determined. This Pilot and Feasibility project is focused on determining the first high-resolution structures of desmosomal cadherins in order to determine the detailed molecular.basis of their cell adhesive function. The cadherin family is characterized by their extracellular cadherin repeat domains (EC1-EC5). It is known that the adhesive function of the cadherin extracellular region is dependent upon the binding of calcium ions between each of these repeat domains which leads to the rigidification of the entire region, however, the specific interfaces and interactions responsible for adhesion are not clearly understood. Some light was shed on this issue recently when the crystal structure of the extracellular domain of C-cadherin was solved by our group. This structure revealed that binding between C-cadherins on opposing cell surfaces most likely occurs when a conserved tryptophan (Trp2) residue of a C-cadherin on one cell intercalates into a hydrophobic pocket, containing highly conserved R-A-L residues, of a C-cadherin on an opposing cell. Further, it was noted that C-cadherins on the same cell surface may interact via a similar mechanism to promote molecular clustering thereby allowing for enhanced adhesion between cells. Both the Trp2 residue and the hydrophobic binding pocket are conserved in desmosomal cadherins, therefore, it seems likely that desmogleins and desmocollins may interact via this same mechanism. However, to date no crystal structure for any of the desmosomal cadherins has been solved. This led us to hypothesize: What is the structure of the adhesive interface of a desmosomal cadherin? How do the adhesive interfaces of desmosomal cadherins interact to contribute to the formation of desmosomes? In order to gain some understanding about the structure of the extracellular domain of desmosomal cadherins, we have embarked on a collaborative effort with Dr. Angela Christiano in the Department of Dermatology at Columbia University to crystallize the extracellular domain of human desmogleins. The goal of this Pilot and Feasibility study is to understand the detailed molecular mechanisms of cadherin function in desmosome intercellular junctions. Dr. Shapiro qualifies under eligibility Category #2 in the Guidelines as an Established Investigator with no previous work in research related to the SDRC. He is an internationally renowned structural biologist who has resolved the structure of many classical cadherins. In this proposal, he will turn his attention to the desmosomal cadherins, central players in skin biology. Dr. Shapiro's P&F study utilizes Cores C and D.
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