Heterotypic interactions among members of the death domain superfamily with implications for p75^NTR-mediated...

The death domain (DD) superfamily, a group of protein interaction modules, plays a crucial role in regulating downstream signaling pathways through the formation of specific complexes. However, the aggregation-prone behavior of many DD superfamily members in solution limits their interaction studies, and the structural mechanisms underlying oligomeric assembly involving different DD subfamilies are not fully understood. Here, we demonstrate that RIP2-CARD retains its native folding and protein function for interacting with the DD of p75 neurotrophin receptor (p75^NTR) in pure water rather than under acidic conditions of pH 5.0 or lower. Leveraging this pure water system, we uncover the heterotypic interactions among p75^NTR-DD, RIP2-CARD, and TRADD-DD, elucidate their ternary HADDOCK complex structure, and identify a new specific binding interface between RIP2-CARD and TRADD-DD. Using developing cortical neurons with endogenous p75^NTR, we demonstrated that co-signaling of the p75^NTR:TRADD:RIP2 tricomplex may shift the signaling balance towards survival by reducing the efficiency of death pathways. Our findings suggest a mechanism in which p75^NTR serves as a molecular scaffold, assembling diverse signaling components to co-activate multiple signaling cascades at the receptor level.