The multiple roles of zinc finger domains

Abstract

Zinc finger (ZnF) domains are prevalent in eukaryotes and play crucial roles in mediating protein-DNA and protein-protein interactions. This Thesis focuses on the molecular details underlying interactions mediated by two ZnF domains. The GATA-1 protein is vital for the development of erythrocytes and megakaryocytes. Pertinent to the protein function is the N-terminal ZnF. In particular, this domain mediates interaction with DNA containing GATC motifs and the coactivator protein FOG. The importance of these interactions was illustrated by the findings in Chapter 3 that naturally occurring mutations identified in patients suffering from blood disorders affect the interaction of the N-terminal ZnF with either DNA (R216Q mutation) or FOG (V205M and G208S mutations). In addition to the interaction FOG makes with GATA-1, it also interacts with the centrosomal protein TACC3. In Chapter 4, this interaction is characterised in detail. The solution structure of the region of FOG responsible for the interaction is determined using NMR spectroscopy, revealing that it is a true classical zinc finger, and characterisation of the interaction domain of TACC3 showed that the region is a dimeric coiled-coil. The FOG:TACC3 interaction appears to be mediated by a-helices from the two proteins. The data presented here represent some of the first described molecular details of how a classical ZnF can contact a protein partner. Interestingly, the a-helix used by the FOG finger to bind TACC3 is the same region utilised by DNA-binding classical zinc fingers to contact DNA. In addition to the multiple roles played by ZnFs, this domain is also known for its robustness and versatility. In Chapter 5, incomplete ZnF sequences were assessed for its ability to form functional zinc-binding domains. Remarkably, CCHX sequences (in the context of BKLF finger 3) were able to form discrete zinc-binding domains and also, mediate both protein-DNA and protein-protein interactions. This result not only illustrates the robust nature of ZnFs, it highlights the need for expanding ZnF sequence criteria when searching for functional zinc-binding modules. Together, the data presented here help further our understanding of zinc finger domains. Similar to the use of DNA-binding ZnFs in designer proteins, these data may start us on the path of designing novel protein-binding ZnFs.