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The protein kinase A holoenzyme is a heterotetramer composed of two types of subunits: Catalytic and Regulatory. The Catalyticsubunit contains the enzyme's active site. It also contains a domain that binds ATP and a domain that binds the regulatory subunit. The Regulatory subunit consists oftwo molecules which bind one another in an anti-parallel orientation to form a homodimer; for type I subunits- this binding is covalent via disulfide bonds. This subunit also has has two domains that bind cyclic AMP, a domain that interacts with a catalytic subunit, and an "auto-inhibitory" domain that serves as a substrate or pseudosubstrate for the catalytic subunit. Regulatory subunits may also have biologic activity distinct from their role in modulating catalytic subunit activity. Regulatory subunits exist in two major forms, RI and RII, with each form having two subtypes designated alpha and beta. Each of the four isotypes of the regulatory subunit is encoded by a different gene. In addition, three isotypes of the catalytic subunit have been identified (alpha, beta and gamma). The different isotypes tend to have different distributions within cells and among tissues. Type I enzymes inhabit cytoplasmic, soluble fractions of the cell, whereas type II enzymes tend to associate with cellular membranes.

Adenylate kinase isoenzyme 5 (AK5) belongs to the adenylate kinase family, which is involved in regulating the adenine nucleotide composition within a cell by catalyzing the reversible transfer of phosphate groups among adenine nucleotides. AK5 is related to the UMP/CMP kinase of several species. AK5 is located in the cytosol and expressed exclusively in the brain.

UCK2 is a member of the uridinekinase family. UCK2 catalyzes the phosphorylation of uridine monophosphate to uridine diphosphate and cytidine monophosphate. UCK2 has a part in the production of pyrimidine nucleoside triphosphates essential for RNA and DNA synthesis. Furthermore, an allele of this gene is an important player in mediating nonhumoral immunity to Hemophilus influenzae type B.

TKT is a thiamine-dependent enzyme that takes part in the channeling of leftover sugar phosphates to glycolysis in the pentose phosphate pathway. Multiple alternatively spliced variants are known that encode the same protein.

GSTK1 is involved in cellular detoxification. GSTK1 is localized to the peroxisome and catalyzes the conjugation of the thiol group of glutathione (GSH) to the electrophilic groups of a broad range of hydrophobic substrates, leading to an easier removal of the latter from the cells.

Serine/threonine-protein kinase 16 (STK16) is a membrane-associated protein kinase which phosphorylates on serine and threonine residues. STK16 is involved in secretory vesicle trafficking or intracellular signaling. Furthermore, the STK16 protein may have a role in regulating stromal-epithelial interactions which occur during ductal morphogenesis in the mammary gland. STK16 can autophosphorylate on Tyr residue; it is however unclear whether STK16 has tyrosine-protein kinase toward other proteins. STK16 may also be involved in TGF-beta signaling.

PI3Ka plays a specific role in apoptosis in human colon cancer cells. Injection of neutralizing antibodies specific to PI3Ka into adenocarcinoma cells induced apoptosis, a response that was reverted by treating cells with caspase inhibitor. It was also shown that PI3Ka mediated phosphorylation of the p85a adapter reduces the lipid kinase activity of the heterodimer and this gives hints for PI3K-dependent signaling events not requiring production of 3’-phosphorylated phosphoinositides.
PI3Ka is a key regulator of the initiation of keratinocyte differentiation. A decrease in PI3Ka activity results in a loss of keratinocyte adhesion to the extracellular membrane and the initiation of early phase differentiation.

CDK16 is a member of the CDK family of serine/threonine protein kinases which are known to regulate the cell cycle. These proteins have a core kinase domain flanked by unique amino- and carboxy- terminal domains. CDK16, which is expressed mainly in mammalian brain, cooperates with an assortment of proteins, and is a part of a multiple signal transduction cascade.

Casein Kinase 2 also called CK2 (also called PKCK2) is a ubiquitous Ser/Thr kinase expressed in all eukaryotes. CK2 is a tetramer composed of two catalytic kinase domains, alpha subunits, and two identical regulatory beta subunits. It has been implicated in cell cycle control, DNA repair, regulation of the circadian rhythm, and other cellular processes. The beta subunit itself does not have kinase activity, but confers stability to the CK2 alpha subunit and is involved in activity and substrate specificity.

Kallikrein-5 (KLK5) is a member of the serine protease family of proteolytic enzymes. KLK5 is expressed in various tissues including the salivary gland, stomach, uterus, lung, thymus, prostate, colon, brain, thyroid, and trachea. KLK5 expression is up-regulated by estrogens and progestins. KLK5 is secreted and may be involved in desquamation in the epidermis. Kallikreins which are a subgroup of serine proteases, have distinct physiological functions. Many kallikreins are associated with carcinogenesis and some have potential as novel cancer and other disease biomarkers. The KLK5 gene is one of the 15 kallikrein subfamily members located in a cluster on chromosome 19.

AK4 belongs to the adenylate kinase family of enzymes. AK4 protein is restricted to the mitochondrial matrix. Adenylate kinases regulate the adenine and guanine nucleotide structures in a cell by catalyzing the reversible transfer of phosphate group among these nucleotides. Hereditary mutations which cause AK4 deficiencies in erythrocytes have been associated to hemolytic anemia.

JUN N-terminal Kinase 2is a member of the MAP kinase family. MAP kinases act as an integration point for multiple biochemical signals, and are involved in a wide variety of cellular processes such as proliferation, differentiation, transcription regulation and development. This kinase targets specific transcription factors, and thus mediates immediate-early gene expression in response to various cell stimuli. It is most closely related to MAPK8, both of which are involved in UV radiation induced apoptosis, thought to be related to the cytochrome c-mediated cell death pathway. This gene and MAPK8 are also known as c-Jun N-terminal kinases. This kinase blocks the ubiquitination of tumor suppressor p53, and thus it increases the stability of p53 in nonstressed cells. Studies of this gene's mouse counterpart suggest a key role in T-cell differentiation. Four alternatively spliced transcript variants encoding distinct isoforms have been reported.

CKB is a cytoplasmic enzyme that takes part in energy homeostasis. CKB enzyme reversibly catalyzes the transfer of phosphate among ATP and various phosphogens such as creatine phosphate. CKB functions as a homodimer in the brain as well as in different tissues, and as a heterodimer with a similar muscle isozyme in heart. Creatine kinases supply the energy of phosphate hydrolysis essential to drive the normal role of many cellular systems including muscle, tumor and cancer cells.

Protein Kinase, AMP-Activated, Alpha 1 (PRKAA1) is a protein coding gene which is the catalytic subunit of AMPK. AMPK is an energy sensor protein kinase which regulates cellular energy metabolism. AMPK adjusts the activity of various important metabolic enzymes by direct phosphorylation. Among its other features, AMPK protects cells from stresses that cause ATP depletion by switching off ATP-consuming biosynthetic pathways.

Testis-specific serine/threonine-protein kinase 6 (TSSK6) is an intronless gene, which belongs to the CAMK Ser/Thr protein kinase family. The TSSK6 protein contains one protein kinase domain. TSSK6 is highly expressed in the testis and lowly expressed in the colon, prostate, thymus, small intestine, and peripheral blood leukocytes. TSSK6 interacts with the heatshock proteins HSPA8, HSPCB, and HAPA1A; these interactions seem to be essential for TSSK6 kinase activity. TSSK6 plays a role in DNA condensation during postmeiotic chromatin remodeling. In addition, TSSK6 is required for sperm production and function.

cAMP-dependent protein kinase inhibitor beta (PKIB) belongs to the cAMP-dependent protein kinase inhibitor family. PKIB may interact with the catalytic subunit of cAMP-dependent protein kinase and function as a competitive inhibitor.

Beta-Glucocerebrosidase, also known as GBA is amember of the glycosyl hydrolase 30 family. GBA is a lysosomal enzyme which requires a signal peptide for transport across the membrane of the rough endoplasmic reticulum as well as glycosylation for transport into lysosomes. Furthermore, Gaucher disease is caused by a deficiency in the activity of the enzyme glucocerebrosidase.

PAK4 is part of the group B family of p21-activated kinases (PAK). It's known as an effector protein for cell division cycle 42(Cdc42) and protein that plays an important role in regulating cytoskeletal organization and cell morphology. PAK4 expression is eminent in many cancer cell lines, and is involved in tumorigenesis. PAK proteins are significant effectors that associate Rho GTPases to cytoskeleton reorganization and nuclear signaling. PAK proteins are targets for the small GTP binding proteins Cdc42 and Rac and have been implicated in a wide range of biological activities. PAK4 cooperates specifically with the GTP-bound form of Cdc42Hs and weakly activates the JNK family of MAP kinases. PAK4 is a mediator of filopodia formation and is involved in the reorganization of the actin cytoskeleton. PAK4 activates the JNK pathway. PAK4 phosphorylates and inactivates the protein phosphatase SSH1, leading to increased inhibitory phosphorylation of the actin binding/depolymerizing factor cofilin. Decreased cofilin activity may lead to stabilization of actin filaments.

Creatine Kinase BB is a cytoplasmic enzyme involved in energy homeostasis. The encoded protein reversibly catalyzes the transfer of phosphate between ATP and various phosphogens such as creatine phosphate. It acts as a homodimer in brain as well as in other tissues, and as a heterodimer with a similar muscle isozyme in heart. The encoded protein is a member of the ATP:guanido phosphotransferase protein family. A pseudogene of this gene has been characterized.

PKLR is a pyruvate kinase which catalyzes the transphosphorylation of phohsphoenolpyruvate into pyruvate and ATP. That is the rate-limiting step of glycolysis. PKLR gene encodes the L- and R-type isoenzymes through alternate splicing events controlled by different promoters. L-type isoform can also appear as a tetramer and is upregulated by glucose with implications in maturity-onset diabetes of the young.

PRKAB2 is a regulatory subunit of the AMP-activated protein kinase (AMPK). AMPK is a heterotrimer contains an alpha catalytic subunit and non-catalytic beta and gamma subunits. AMPK is a significant energy-sensing enzyme that supervises cellular energy status. AMPK is activated as a reply to cellular metabolic stresses, therefore phosphorylates and inactivates acetyl-CoA carboxylase (ACC) and beta-hydroxy beta-methylglutaryl-CoA reductase (HMGCR), vital enzymes involved in regulating de novo biosynthesis of fatty acid and cholesterol. PRKAB2 is a positive regulator of AMPK activity and highly expressed in skeletal muscle.

The Casein kinase 2 (EC2.7.11.1) is a serine/threonine-selective protein kinasethat is a tetramer of two alpha subunits and two beta subunits. The alpha subunits have the catalytic kinase domain. Casein kinase 2 has been implicated in cell cyclecontrol, DNA repair, regulation of the circadian rhythmand other cellular processes.
Casein kinase 2 activity has been reported to be activated following Wnt signaling pathwayactivation. A Pertussis toxin-sensitive G proteinand Disheveled appear to be an intermediary between Wnt-mediated activation of the Frizzled receptor and activation of casein kinase 2.

Adenylate kinases play a role in regulating the adenine nucleotide composition within a cell by catalyzing the reversible transfer of phosphate groups among adenine nucleotides. There are 3 types of adenylate kinase isozymes, AK1, AK2, and AK3 in vertebrates. Expression of these isozymes are tissue-specific and developmentally regulated. AK2 is localized in the mitochondrial intermembrane space and is involved in apoptosis. AK2 is mutated in individuals with reticular dysgenesis.