Protein kinase can be classified by catalytic domains, including AGC kinase, CAMK kinase, CK1 kinase, CMGC kinase, STE kinase, TK kinase, TKL kinase and RGC kinase
Casein kinase has been widely used for decades to denote protein kinases sharing the ability to readily phosphorylate casein. The casein kinases (CK) belong to the serine/threonine kinases. There are two main classes: casein kinase 1 (CKI) and casein kinase 2 (CK2).
CMGC kinase family is named after the initials of its subfamily members, including cyclin-dependent kinase (CDK), mitogen-activated protein kinase (MAPK), glycogen synthase kinase (GSK) and CDC-like kinase (CLK). There are also other CMGC subfamilies, including DYRK and SRPK. CMGC kinase family has 63 family members. CMGC kinases are highly conserved across organisms.
STE kinase consists of three main families which sequentially activate each other to then activate the MAPK family. The STE7 family directly phosphorylate MAPKs, and are also known as MAP2K, MEK, or MKKs; STE11 members phosphorylate STE7 kinases and are called MAP3K, while many STE20 members (MAP4K) act on Ste11 kinases.