Characterisation of the bir domain

Apoptosis is the process whereby unwanted or damaged cells are removed from an organism. The process is initiated by numerous stimuli which trigger an array of effector cysteine proteases. The signalling and activation pathways that connect cell death stimuli to apoptosis effector mechanisms have not been fully elucidated. One family of proteins involved in connecting stimuli to ef fector mechanisms is the Inhibitor of Apoptosis (IAP) class. lAPs were first identified as genes expressed by baculovires upon invasion of an insect cell. All IAP proteins contain several copies of the Baculoviral IAP Repeat (BIR) motif. lAPs are highly conserved across a number of species suggesting that they have an important function. In mammalian cells IAP proteins (e.g C-IAP2/MIHB) are found in association with the TNF receptor (p75). lAPs do not interact directly with the TNF receptor, instead they associate with TNF Receptor Associated Factors (TRAF). The TRAF/IAP interaction is mediated by the BIR motif in IAP proteins. The BIR motif has not been previously characterised although it contains a conserved CX2CX,6HX6C sequence which is suggestive of zinc binding. The aim of this project is to ascertain if the BIR motif is a stable folded domain and if so to determine the three dimensional structure. A single BIR motif from MIHB/C-IAP2 has been expressed in E.coli and purified to homogeneity. Our results indicate that the BIR motif is a discrete structural domain. We now hope to determine the three dimensional structure of this domain. Supported by the Foundation for Research Science and Technology, \pw Zealand.