| The Role of the SPRY Domain in the SPRY Domain-Containing SOCS Box Proteins (2005) | |||||||||||
Abstract | |||||||||||
| There are four mammalian SSB proteins (SSB-1 to -4), and these are characterized by a C-terminal SOCS box and central SPRY domain. The C-terminal SOCS box was first observed in proteins that were found to act as Suppressors of Cytokine Signalling and function by virtue of their SH2 domain. Other families containing the SOCS box motif were defined by the domains N-terminal to this, such as the ASBs (Ankyrin repeats), WSBs (WD40 repeats) and of course the SSBs (SPRY domains). This thesis describes a very broad investigation of the SSBs, a protein family about which very little was known. To begin with, functional investigation into the evolution of this family and analysis of murine SSB expression patterns was performed. This highlighted that the family was highly conserved and had differential expression in the mouse, suggestive of important, unique functional roles for the individual family members. The majority of work in the thesis then proceeds in three directions; (i) analysis of the SSB proteins in vivo, with genetic deletion of SSB-2 in the mouse, (ii) biochemically, with analysis of SSB binding partners, and (iii) structurally, with functional analysis of the structure of SSB-2. In vivo murine SSB-2 was found to be required for the maintenance of two homeostatic parameters, the platelet count and Blood Urea Nitrogen (BUN) level. Its deletion was also associated with the development of epileptic seizures and premature death of mice. Biochemical analyses determined that SSB-1, -2 and -4 but not SSB-3 interact specifically and directly with the Prostate Apoptosis Response protein –4 (Par-4). This interaction appeared to result in the ubiquitination of Par-4, and the implications of this interaction are discussed in the context of the SSB-2-/- mouse phenotype. The first structure of a SPRY domain is also presented, as from the NMR structure of SSB-2. Structure/function studies defined conserved residues within this SPRY domain that are required to bind Par-4. The structure of SSB-2 also proved to be a novel fold and may have more general implications for the function of other SPRY domains, some of which are implicated in human diseases. | |||||||||||
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