Protein kinase domain

The protein kinase domain is a structurally conserved protein domain containing the catalytic function of protein kinases. Protein kinases are a group of enzymes that move a phosphate group onto proteins, in a process called phosphorylation. This functions as an on/off switch for many cellular processes, including metabolism, transcription, cell cycle progression, cytoskeletal rearrangement and cell movement, apoptosis, and differentiation. They also function in embryonic development, physiological responses, and in the nervous and immune system. Abnormal phosphorylation causes many human diseases, including cancer, and drugs that affect phosphorylation can treat those diseases.

Protein kinases possess a catalytic subunit which transfers the gamma phosphate from nucleoside triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function. These enzymes fall into two broad classes, characterised with respect to substrate specificity: serine/threonine specific and tyrosine specific.

Function
Protein kinase function has been evolutionarily conserved from Escherichia coli to Homo sapiens. Protein kinases play a role in a mulititude of cellular processes, including division, proliferation, apoptosis, and differentiation. Phosphorylation usually results in a functional change of the target protein by changing enzyme activity, cellular location, or association with other proteins.

Structure
The catalytic subunits of protein kinases are highly conserved, and several structures have been solved, leading to large screens to develop kinase-specific inhibitors for the treatments of a number of diseases.

Eukaryotic protein kinases  are enzymes that belong to a very extensive family of proteins which share a conserved catalytic core common with both serine/threonine and tyrosine protein kinases. There are a number of conserved regions in the catalytic domain of protein kinases. In the N-terminal extremity of the catalytic domain there is a glycine-rich stretch of residues in the vicinity of a lysine residue, which has been shown to be involved in ATP binding. In the central part of the catalytic domain there is a conserved aspartic acid residue which is important for the catalytic activity of the enzyme.

Examples
The following is a list of human proteins containing the protein kinase domain:

AAK1;     ABL1;    ABL2;    ACVR1;     ACVR1B;    ACVR1C;    ACVR2A;    ACVR2B;    ACVRL1;    ADCK1;   ADCK2;   ADCK3;   ADCK4;    ADCK5;     ADRBK1; ADRBK2;   AKT1;      AKT2;      AKT3;      ALPK1;      ALPK2;      ALPK3;      STRADB;   CDK15;   AMHR2;     ANKK1; ARAF;     ATM;      ATR;    AURKA;     AURKB;     AURKC;     AXL;   BCKDK;   BLK;    BMP2K;     BMPR1A;    BMPR1B;    BMPR2;   BMX; BRAF;     BRSK1;     BRSK2;     BTK;     BUB1;      C21orf7;    CALM1;  CALM2;  CALM3;   CAMK1;     CAMK1D;    CAMK1G; CAMK2A;   CAMK2B;    CAMK2D;    CAMK2G;    CAMK4;     CAMKK1;    CAMKK2;    CAMKV; CASK;     CDK20;      CDK1;      CDK11B;    CDK11A;    CDK13;    CDK19;    CDC42BPA; CDC42BPB; CDC42BPG;  CDC7;      CDK10;     CDK2;      CDK3;      CDK4;      CDK5; CDK6;     CDK7;      CDK8;      CDK9;      CDK12;     CDK14;     CDK16;     CDK17;     CDK18;     CDKL1;     CDKL2;     CDKL3;     CDKL4;     CDKL5; CHEK1;    CHEK2;     CHUK;      CIT;       CKB;    CKM;    CLK1;      CLK2;      CLK3; CLK4;     CSF1R;     CSK;       CSNK1A1;   CSNK1A1L;  CSNK1D;    CSNK1E;    CSNK1G1;   CSNK1G2; CSNK1G3;  CSNK2A1;   CSNK2A2;   DAPK1;     DAPK2;     DAPK3;     DCLK1; DCLK2;    DCLK3;     DDR1;    DDR2;      DMPK;      DYRK1A;    DYRK1B;    DYRK2;     DYRK3;     DYRK4; EGFR;     EIF2AK1;   EIF2AK2;   EIF2AK3;   EIF2AK4;   ELK1;    EPHA1;   EPHA2;   EPHA3;   EPHA4;   EPHA5;   EPHA6;   EPHA7;   EPHA8;   EPHB1;   EPHB2;   EPHB3;   EPHB4;   ERBB2;    ERBB3;    ERBB4;    ERN1;      ERN2;   FER;    FES;      FGFR1;   FGFR2;    FGFR3;     FGFR4;     FGR;   FLT1;   FLT3;    FLT4;    FYN;   GAK;       GRK1;      GRK4; GRK5;     GRK6;      GRK7;      GSK3A;     GSK3B;     GUCY2C;    GUCY2D;    GUCY2E;    GUCY2F; HCK;    HIPK1;     HIPK2;     HIPK3;     HIPK4;     HUNK;      ICK;       IGF1R;   IGF2R;   IKBKB;     IKBKE; ILK;   INSR;    IRAK1;     IRAK2;     IRAK3;     IRAK4;     ITK;    JAK1;   JAK2;    JAK3;    KALRN;     KDR;   SIK3;  KSR2;      LATS1; LATS2;    LIMK1;     LCK;    LIMK2;     LRRK1;     LRRK2;     LYN;     MAK; MAP2K1;   MAP2K2;    MAP2K3;    MAP2K4;    MAP2K5;    MAP2K6;    MAP2K7;    MAP3K1; MAP3K10;  MAP3K11;   MAP3K12;   MAP3K13;   MAP3K14;   MAP3K15;   MAP3K2;    MAP3K3; MAP3K4;   MAP3K5;    MAP3K6;    MAP3K7;    MAP3K8;    MAP3K9;    MAP4K1;    MAP4K2; MAP4K3;   MAP4K4;    MAP4K5;    MAPK1;     MAPK10;    MAPK12;    MAPK13;    MAPK14; MAPK15;   MAPK3;     MAPK4;     MAPK6;     MAPK7;     MAPK8;     MAPK9;     MAPKAPK2; MAPKAPK3; MAPKAPK5;  MARK1;     MARK2;     MARK3;     MARK4;     MAST1;     MAST2; MAST3;    MAST4;     MASTL;     MELK;      MERTK;    MET;    MINK1; MKNK1;    MKNK2;     MLKL;      MOS;       MST1R;      MST4;      MTOR;    MYLK; MYLK2;    MYLK3;     MYLK4;     NEK1;      NEK10;     NEK11;     NEK2; NEK3;     NEK4;      NEK5;      LOC100506859;  NEK6;      NEK7;      NEK8;      NEK9;      MGC42105; NLK;      NRK;       NTRK1;     NTRK2;     NTRK3;     NUAK1;     NUAK2;     OBSCN;     OXSR1; PAK1;     PAK2;      PAK3;      PAK4;      PAK6;      PAK7;      PASK;      PBK; PDGFRA;   PDGFRB;    PDIK1L;    PDPK1;     PHKA1;     PHKB;     PHKG1; PHKG2;    PIK3R4;    PIM1;      PIM2;      PIM3;      PINK1;     PKMYT1;    PKN1; PKN2;     PKN3;      PLK1;      PLK2;      PLK3;      PLK4;      PNCK;      PRKAA1; PRKAA2;   PRKACA;    PRKACB;    PRKACG;    PRKCA;     PRKCB;    PRKCD;     PRKCE; PRKCG;    PRKCH;     PRKCI;     PRKCQ;     PRKCZ;     PRKD1;     PRKD2; PRKD3;    PRKG1;     PRKG2;     PRKX;      LOC389906;  PRKY;      PRPF4B;    PSKH1;     PSKH2;    PTK2;   PTK2B;     RAF1;      RAGE;      RET;    RIP3;      RIPK1;     RIPK2;     RIPK3;     RIPK4; ROCK1;    ROCK2;     ROR1;    ROR2;    ROS1;   RPS6KA1;   RPS6KA2;   RPS6KA3; RPS6KA4;  RPS6KA5;   RPS6KA6;   RPS6KB1;   RPS6KB2;   RPS6KC1;   RPS6KL1;   RYK;   SCYL1; SCYL2;    SCYL3;     SGK1;       LOC100130827;    SGK196; SGK2;     SGK3;      SGK494;    SIK1;      SIK2;      SLK; SNRK;     SPEG;      SRC;    SRPK1;     SRPK2;     SRPK3;     STK10;     STK11;     STK16; STK17A;   STK17B;    STK19;    STK24;     STK25;     STK3;      STK31;     STK32A;    STK32B; STK32C;   STK33;     STK35;     STK36;     STK38;     STK38L;    STK39;     STK4; STK40;    SYK;      TAOK1;     TAOK2;     TAOK3;     TBCK;      TBK1;     TEC; TESK1;    TESK2;     TGFBR1;    TGFBR2;    TIE1;      TIE2;      TLK1;      TLK2;      TNIK;    TNK1;   TNK2; TSSK1B;    TSSK2;     TSSK3;     TSSK4;    TTBK1;     TTBK2;     TTK;  TWF2; TXK;    TYK2;     TYRO3;     UHMK1;     ULK1;      ULK2; ULK3;     ULK4;      VRK1;      VRK2;      VRK3;     WEE1;      WEE2;     WNK1;      WNK2; WNK3;     WNK4;      YES1;       ZAK;    ZAP70;