Both serine/threonine and tyrosine protein kinases share a catalytic core with the protein kinase (IPR011009). A nucleotide binding site and catalytic apparatus are found in the interlobular cleft of the catalytic domain. Phosphate groups are chemically added to some proteins to alter them. The PI3K catalytic domain phosphorylates phosphoinositide and is thus involved in many fundamental cellular processes, including apoptosis, proliferation, motility, and adhesion. PK_Ty_Ser-Thr, or IPR001245, is a serine-threonine kinase Both serine/threonine and tyrosine protein kinases contain catalytic domains.