Dynamic molecular architecture and substrate recruitment of cullin3-RING E3 ligase CRL3^KBTBD2

Phosphatidylinositol 3-kinase alpha, a heterodimer of catalytic p110 alpha and one of five regulatory subunits, mediates insulin- and insulin like growth factor-signaling and, frequently, oncogenesis. Cellular levels of the regulatory p85 alpha subunit are tightly controlled by regulated proteasomal degradation. In adipose tissue and growth plates, failure of K48-linked p85 alpha ubiquitination causes diabetes, lipodystrophy and dwarfism in mice, as in humans with SHORT syndrome. Here we elucidated the structures of the key ubiquitin ligase complexes regulating p85 alpha availability. Specificity is provided by the substrate receptor KBTBD2, which recruits p85 alpha to the cullin3-RING E3 ubiquitin ligase (CRL3). CRL3(KBTBD2) forms multimers, which disassemble into dimers upon substrate binding (CRL3(KBTBD2)-p85 alpha) and/or neddylation by the activator NEDD8 (CRL3(KBTBD2)similar to N8), leading to p85 alpha ubiquitination and degradation. Deactivation involves dissociation of NEDD8 mediated by the COP9 signalosome and displacement of KBTBD2 by the inhibitor CAND1. The hereby identified structural basis of p85 alpha regulation opens the way to better understanding disturbances of glucose regulation, growth and cancer.