Serine/threonine-specific protein kinase

Serine/threonine protein kinases phosphorylate the OH group of serine or threonine (which have similar sidechains).

At least 125 of the 500+ human protein kinases are serine/threonine kinases (STK).

Selectivity
While serine/threonine kinases all phosphorylate serine or threonine residues in their substrates, they select specific residues to phosphorylate on the basis of residues that flank the phosphoacceptor site, which together comprise the consensus sequence. Since the consensus sequence residues of the substrate to be phosphorylated make contact with the catalytic cleft of the kinase at several key amino acids (usually through hydrophobic forces and ionic bonds), a kinase is usually not specific to a single substrate, but instead can phosphorylate a whole "substrate family" having common recognition sequences. While the catalytic domain of these kinases is highly conserved, the sequence variation that is observed in the kinome (the subset of genes in the genome that encode kinases) provides for recognition of distinct substrates. Most kinases are inhibited by a pseudosubstrate that binds to the kinase like a real substrate but lacks the amino acid to be phosphorylated. When the pseudosubstrate is removed, the kinase can perform its normal function.

EC numbers
Many serine/threonine protein kinases do not have their own individual EC numbers and use "2.7.11.1". These were formerly included in EC number "2.7.1.37", which was a general EC number for any enzyme that phosphorylates proteins while converting ATP to ADP (i.e., ATP:protein phosphotransferases.)

Types
Types include those acting directly as receptors (Receptor protein serine/threonine kinase) and Intracellular signaling peptides and proteins. Of the latter, types include:

Clinical significance
Serine/threonine kinase (STK) expression is altered in many types of cancer.

Serine/threonine protein kinase p90-kDa ribosomal S6 kinase (RSK) is in involved in development of some prostate cancers.

Raf inhibition has become the target for new anti-metastatic cancer drugs as they inhibit the MAPK cascade and reduce cell proliferation.