Glycosphingolipids (GSL)-enriched 'rafts'and caveolae are membrane microdomains that putatively function as lateral organizing sites for signaling proteins involved in oncogenesis. Because the overexpression of select caveolar proteins, i.e. caveolin-1, is associated with tumor cell survival, aggression and metastatic potential, targeting GSL-enriched caveolae may prove useful as a new therapy for the functional disruption of metastatis, tumorigenesis, and tumor progression. The processes by which GSL-enriched domains are formed and maintained are not well defined but are expected to involve specific proteins that can bind and transfer GSLs between and within cells. Our objective is to elucidate the structure of human glycolipid transfer protein (GLTP) and related orthologs and to identify/-characterize folding domains responsible for glycolipid liganding selectivity using structural, dynamical, and mutational approaches by taking advantage of the structural expertise of the Dinshaw Patel (Sloan-Kettering Institute, NY) and the molecular biological and glycosphingolipid expertise of the Rhoderick Brown (Hormel Institute, MN) laboratories. The rationale for the research is that, solving the structure of GLTP and related orthologs in their apo and glycolipid-liganded states will enable mapping of the protein domains and associated key amino acid residues involved in GLTP functionality. Acquiring this knowledge will provide a foundation for pursuing the future development of pharmacologic agents that can specifically target GLTP in oncogenic cells displaying aberrant GLTP activity. The proposed work is innovative because it capitalizes on the first-ever, structural insights into human GLTP. The novel two-layer, all alpha helical topology of GLTP differs distinctly from the folding topologies of other known lipid binding/transfer proteins, suggesting that the GLTP folding motif defines a novel family of proteins. The studies will take advantage of our recent successes in the molecular cloning and expression of GLTP and related point mutants. It is our expectation that the proposed structural-dynamics-mutational studies of human GLTPs and related orthologs will provide unparalleled insights into the functional workings of this emerging new protein family. This new knowledge is expected to be significant by providing a foundation for using GLTP in new and innovative ways, such as introducing specific GSL antigens into cancer cells to help achieve targeted destruction of diseased cells via immunotherapeutic means.
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