Structure of the phosphoinositide 3-kinase p110γ-p101 complex reveals molecular mechanism of GPCR activation

<jats:title>Abstract</jats:title><jats:p>The class IB phosphoinositide 3-kinase (PI3K), PI3Kγ, is a master regulator of immune cell function, and a promising drug target for both cancer and inflammatory diseases. Critical to PI3Kγ function is the association of the p110γ catalytic subunit to either a p101 or p84 regulatory subunit, which mediates activation by G-protein coupled receptors (GPCRs). Here, we report the cryo-EM structure of a heterodimeric PI3Kγ complex, p110γ-p101. This structure reveals a unique assembly of catalytic and regulatory subunits that is distinct from other class I PI3K complexes. p101 mediates activation through its Gβγ binding domain, recruiting the heterodimer to the membrane and allowing for engagement of a secondary Gβγ binding site in p110γ. Multiple oncogenic mutations mapped to these novel interfaces and enhanced Gβγ activation. A nanobody that specifically binds to the p101-Gβγ interface blocks activation providing a novel tool to study and target p110γ-p101-specific signaling events <jats:italic>in vivo</jats:italic>.</jats:p>