PI3Ks are classified into three groups: class I, class II and class III. Class I PI3Ks are heterodimers consisting of a catalytic p110 subunit and a p85 regulatory subunit. The class I PI3Ks are further divided into class IA and class IB subgroups. Class IA PI3Ks consist of PI3Kα, PI3Kβ and PI3Kδ with p110α, p110β, and p110δ as their catalytic subunit respectively. The catalytic subunit can form a heterodimer with any of the p85 subunit (p85α, p85β, p55α, p50α and p55γ). The class IB PI3K subgroup consists of a p110γ catalytic subunit and one of the regulatory subunits (p101, p87 and p84). The class II and III PI3Ks consist of only a catalytic polypeptide. Several different domains are present including SH3: Src homology 3 domain; BHD: BCR homology domain; SH2: Src homology 2 domain; iSH2: Inter-Src homology 2 domain; p110γ BD: p110γ binding domain; Gβγ BD: G beta gamma protein complex binding domain; PX: phosphoinositide-binding structural domain.