This subfamily is composed of unusual homoserine kinases, from a subset of bacteria, which have a Protein Kinase fold. These proteins do not bear any similarity to the GHMP family homoserine kinases present in most bacteria and eukaryotes. Homoserine kinase catalyzes the transfer of the gamma-phosphoryl group from ATP to L-homoserine producing L-homoserine phosphate, an intermediate in the production of the amino acids threonine, methionine, and isoleucine. The Type II homoserine kinase subfamily is part of a larger superfamily that includes the catalytic domains of other kinases, such as the typical serine/threonine/tyrosine protein kinases (PKs), RIO kinases, actin-fragmin kinase (AFK), and phosphoinositide 3-kinase (PI3K).
Jiyao W et al.(2023). "The conserved domain database in 2023.",