This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Tumor necrosis factor receptors are cytokine receptors important in cellular signaling. CD40 is a well-characterized member of this family that is expressed on B cells and triggers immune responses, immunoglobulin class switching and activation of apoptosis. Like CD40, other TNFRs, such as LTbeta receptor and BAFF receptor, as well as the oncoprotein LMP1 from Epstein Barr Virus, associate with the cytoplasmic domain of TRAFs to stimulate cell signals. In a continuing series, we are crystallizing TRAF3 bound in complex with the functional fragments of each of these signaling partners. To study the details of binding and define the molecular basis for signaling, synthetic peptides representing the interacting regions are soaked into TRAF3 crystals. The crystals do not typically diffract with a standard rotating anode source to the level of resolution required for detailed binding analyses. Therefore we plan to continue using synchrotron x-rays to collect data for the complexes.