The mammalian pseudokinase SgK223, and its structurally-related homologue SgK269, are oncogenic scaffolds that nucleate the assembly of specific signaling complexes and regulate tyrosine kinase signalling. Both scaffolds are implicated in specific human malignancies: SgK223 in pancreatic ductal adenocarcinoma (PDAC) progression and SgK269 in colon and breast cancer as well as PDAC. Previously, we demonstrated that these proteins form homo- and hetero-oligomers in vitro and in cells, a mechanism that underpins a diversity of signalling outputs . However, how these two scaffolds organise specific signalling complexes to regulate contrasting cellular responses remains largely uncharacterised.
To gain mechanistic insights into how these enzymatically-dead pseudokinases regulate oncogenic signal transduction networks, we recently determined the structure of SgK223 pseudokinase domain and its adjacent N- and C-terminal helices. Our structure uncovers how the N- and C-regulatory helices engage in a novel fold to mediate the assembly of a high-affinity dimer. In addition, we identified regulatory interfaces on the pseudokinase domain required for the self-assembly of large open-ended oligomers. This study highlights the remarkable diversity in how the kinase fold mediates non-catalytic functions and provides mechanistic insights into how the assembly of these two oncogenic scaffolds is achieved in order to regulate signaling output .