ID: 95: Quantitative characterisation of STAT2 dimerisation

Abstract

Interferons (IFN) are released by cells as a response to microbial infection. They are best known for their antiviral and immunomodulatory functions. IFNs bind to cell surface receptors which then initiate a signalling cascade inside the cell, ultimately resulting in target gene transcription. Essential to this signalling cascade is the dimersation of signal transducer and activator of transcription proteins (STATs). The composition of these dimers determines the genes targeted. The STAT proteins, which are encoded by 7 different genes, can function as homodimers with the possible exception of STAT2. We will generate quanititative data on STAT2 homodimerisation to clarify this question. It is well known, in contrast, that STAT2 heterodimerises with STAT1. In fact, STAT1-STAT2 heterodimers are crucial for type I IFN signalling. STAT heterodimerisation is a commonly observed phenomenon that is nonetheless poorly understood. Our study will assess the interaction of STAT1 with STAT2 and thus for the first time generate quantitative data on the heterodimerisation of STAT proteins. We will utilise recombinant STAT1- and STAT2-proteins produced in insect cells, purified with affinity chromatography and gel filtration. Subsequently these proteins will be subject to sedimentation velocity and sedimentation equilibrium experiments using an analytical ultracentrifuge. These powerful methods allow quantitative characterisation of single- and multi-protein interactions, such as homodimer and heterodimer assembly respectively. These studies will further our understanding of STAT dimerisation and hence IFN signalling.