Tyson Shepherd

Mentor: Ernesto Fuentes, PhD

Year Entered Into Program: 2006-2011

PhD Institution: University of uppsala, Uppsala, Sweden

Research Description

T-cell lymphoma Invasion and Metastasis 1 (Tiam1) protein is a Guanine Exchange Factor (GEF) that specifically activates the Rho-family GTPase Rac1. In mammalian cells, spacial and temporal regulation is achieved via several distinct protein-protein interaction domains. The Fuentes Lab applies biophysical techniques to understand how each of these domains contribute to Tiaim1 activity. Included in this set of domains is a Ras Binding (RB) domain just N-terminal to a Post-synaptic density-95/Discs large/Zonula occludens-1 (PDZ) domain. Tiam1 GEF activity is thought to increase upon activated Ras binding to the RB domain, while the functional importance of the PDZ domain remains a mystery. My research is directed at understanding the structural and functional relationship between these two domains both alone and in the context of the full length Tiam1. To understand these domains further, we express each domain separately and together with various surrounding domains. The structure of the PDZ domain was solved in both free form and bound to model peptide ligand. Nuclear magnetic resonance was used to check the binding affinity of the ligand and to investigate intermolecular dynamics upon peptide binding. Further structure and function work will be carried out on neighboring domains in the Tiam1 protein. We are also examining the effect of mutations in the binding pocket of the PDZ domain contained within the full-length Tiam1 in vivo.


Clark, B.K., Rosa, E.R., Hall, A.D., Shepherd, T.R.:  Dynamics of an Electronic Impact. Oscillator. Phys. Lett. A. 318, 514-521, 2003. Shepherd, T.R., Klaus, S.M., Liu, X., Ramaswamy, S., DeMali, K.A., and Fuentes, E.J. (2010). The Tiam1 PDZ Domain Couples to Syndecan1 and Promotes Cell-Matrix Adhesion, J. Mol. Biol. 398:730-746, 2010. Shepherd, T.R. and Fuentes, E.J.:  Structural and Thermodynamic Analysis of PDZ/ Ligand Interactions. Methods in Enzymology, In Press 2010. Shepherd, T.R., Hard, R.L., Murray, A.M., Pei, D., Fuentes, E.J. (2010). Distinct Ligand Specificity of the Tiam1 and Tiam2 PDZ Domains. Biochemistry, Submitted.  


  • First Year Graduate Research Award, 2007
  • Best Poster Award, 46th Annual MIKI Conference, 2008
  • Best Presentation award, GRASP-NMR Conference, 2009
  • Dr. Lois Bigger Gehring Award, 2009
  • Biochemistry Retreat Poster Award, 2010
  • Center for Biocatalysis and Bioprocessing NIH Predoctoral Fellowship, 2009-2011