HDX-MS was used to map the changes in conformational dynamics in the catalytic subunit of PI3Ka, p110a, in complex with the following five reguatory subunits: p85a, p85b, p55g, p55a, p50a. Apo and pY activated states were also compared between the three splice variants encoded by PIK3R1. No significant changes were observed in p110a between any of the regulatory subunits in the apo state.