Huntingtin Protein Proline-rich Region With Sh3 And Dual-ww Domain Interaction

This PhD thesis focuses on the specific interactions of proline-rich region (PRR) in Huntingtin (Htt) protein with SH3GL3-SH3 domain and HYPA-WW1-2 domain pair (Chapter 1). We also determined the solution structure of the ubiquitin-like domain (UbL) of DC-UbP (Chapter 2).Huntington's disease (HD) is an inherited, progressive, neurodegenerative disease and is caused by a CAG repeat expansion in the huntingtin gene encoding the Htt protein.. Human Htt is a large protein comprising 3144 amino-acid residues but with unknown biological function. Currently, several Htt-interacting proteins have been identified that might be associated with the normal function of Htt and/or involved in the pathology of Huntington's disease. A large number of the Htt-interacting proteins have been found to bind to the PRR segment through their SH3 and WW domains.We have investigated the specific interactions of Htt PRR with the SH3GL3-SH3 domain and HYPA-WW1-2 domain pair by NMR techniques. The results show that Htt PRR recognizes the SH3 and WW1-2 domains with high specificities but with different mechanisms. Htt PRR binds with the SH3 domain through its nearly entire chain, and the binding region on the domain includes the canonical PxxP-binding site and the specificity pocket. The C-terminus of PRR orients to the specificity pocket whereas the N-terminus to the PxxP-binding site. Htt PRR can also specifically bind to WW1-2 through its N-terminal portion preferential to WW1 and the C-terminal to WW2. This study provides structural insights into the specific interactions between Htt PRR and its binding partners, which may have implications for the understanding of HD.The dendritic cell-derived ubiquitin-like protein (DC-UbP) was implicated in cellular differentiation and apoptosis. We have determined the solution structure of the UbL domain of DC-UbP. One distinct feature of the domain structure is its highly positively charged surface that is different from the corresponding surfaces of the well-known UbL modifiers: Ub, NEDD8 and SUMO-1. The key amino-acid residues responsible for guiding polyubiquitinated proteins to proteasome degradation in Ub are not conserved in the UbL domain. This implies that the UbL domain of DC-UbP may have its own specific interaction partners with other yet unknown cellular functions related to the Ub pathway.