BCKDK
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Branched chain ketoacid dehydrogenase kinase (BCKDK) is an
enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
encoded by the BCKDK
gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
on
chromosome 16 Chromosome 16 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 16 spans about 90 million base pairs (the building material of DNA) and represents just under 3% of the total DNA in cel ...
. This enzyme is part of the mitochondrial
protein kinases A protein kinase is a kinase which selectively modifies other proteins by covalently adding phosphates to them (phosphorylation) as opposed to kinases which modify lipids, carbohydrates, or other molecules. Phosphorylation usually results in a fun ...
family and it is a regulator of the
valine Valine (symbol Val or V) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated −NH3+ form under biological conditions), an α- carboxylic acid group (which is in the deproton ...
,
leucine Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α-Car ...
, and
isoleucine Isoleucine (symbol Ile or I) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid group (which is in the depro ...
catabolic pathways. BCKDK is found in the
mitochondrial matrix In the mitochondrion, the matrix is the space within the inner membrane. It can also be referred as the mitochondrial fluid. The word "matrix" stems from the fact that this space is viscous, compared to the relatively aqueous cytoplasm. The mitoc ...
and the prevalence of it depends on the type of
cell Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a de ...
.
Liver cells A hepatocyte is a cell of the main parenchymal tissue of the liver. Hepatocytes make up 80% of the liver's mass. These cells are involved in: * Protein synthesis * Protein storage * Transformation of carbohydrates * Synthesis of cholesterol, bile ...
tend to have the lowest concentration of BCKDK, whereas skeletal muscle cells have the highest amount. Abnormal activity of this enzyme often leads to diseases such as
maple syrup urine disease Maple syrup urine disease (MSUD) is a rare, inherited metabolic disorder that affects the body's ability to metabolize amino acids due to a deficiency in the activity of the branched-chain alpha-ketoacid dehydrogenase (BCKAD) complex. It parti ...
and
cachexia Cachexia () is a syndrome that happens when people have certain illnesses, causing muscle loss that cannot be fully reversed with improved nutrition. It is most common in diseases like cancer, Heart failure, congestive heart failure, chronic o ...
.


Structure

BCKDK's structure consists of a characteristic
nucleotide Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...
-binding domain along with a four-helix bundle domain similar to certain aspects of protein histidine kinases, which are involved in two-component signal transduction systems. BCKDK is also a dimer with a Leu389 residue located between the dimers and this dimerization is seen to be essential for its kinase activity and
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
stability. Moreover, it is made up of 382
amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the Proteinogenic amino acid, 22 α-amino acids incorporated into p ...
and has a
molecular weight A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
of 43 kDa. The gene ''BCKDK'' is located at 16p11.2, has an
exon An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequence ...
count of 11, and it lacks a TATA-box and an
initiator element The initiator element (''Inr''), sometimes referred to as initiator motif, is a core promoter that is similar in function to the Pribnow box (in prokaryotes) or the TATA box (in eukaryotes). The ''Inr'' is the simplest functional promoter that i ...
.


Function

BCKDK regulates the activity of branched-chain α-ketoacid dehydrogenase complex (BCKD) through
phosphorylation In biochemistry, phosphorylation is described as the "transfer of a phosphate group" from a donor to an acceptor. A common phosphorylating agent (phosphate donor) is ATP and a common family of acceptor are alcohols: : This equation can be writ ...
and inactivation. This inactivation results in increased
branched-chain amino acids A branched-chain amino acid (BCAA) is an amino acid having an aliphatic side-chain with a branch (a central carbon atom bound to three or more carbon atoms). Among the proteinogenic amino acids, there are three BCAAs: leucine, isoleucine, and va ...
(BCAA), which is seen to reduce oxidative stress; however, having too much BCAA has been proven to be toxic to humans. Therefore, BCKDK is a vital tool to assist with BCAA homeostasis. As stated earlier, BCKDK concentrations vary depending on the type of tissue that is observed, whereas BCKD's concentration is the same in any tissue. Although BCKD concentration is constant, the amount of BCKDK determines the activity of the dehydrogenase complex. Since liver tissue is seen to have the lowest concentration of BCKDK, the activity of BCKD is seen to be the highest, delineating the fact that the BCKD kinase inversely affects the BCKD activity.


Clinical significance

Abnormalities in BCKD activity often leads to pathological conditions which is why BCKDK is needed to regulate it. Often,
mutations In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitosi ...
in the ''BCKDK'' gene occur creating the deviation in BCKD behavior. Exceedingly high BCKD complex activity increases branched-chain amino acid catabolism and protein degradation in skeletal muscle, which is a distinctive feature for cachexia. Deficiencies in BCKD activity have been the main cause in the rare metabolism maple syrup urine disease that can lead to
mental retardation Intellectual disability (ID), also known as general learning disability (in the United Kingdom), and formerly mental retardation (in the United States), Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010).Archive is a generalized neurodevelopmental ...
, brain edema,
seizures A seizure is a sudden, brief disruption of brain activity caused by abnormal, excessive, or synchronous neuronal firing. Depending on the regions of the brain involved, seizures can lead to changes in movement, sensation, behavior, awareness, o ...
,
coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...
, and
death Death is the end of life; the irreversible cessation of all biological functions that sustain a living organism. Death eventually and inevitably occurs in all organisms. The remains of a former organism normally begin to decompose sh ...
if not treated correctly by lifelong limitation of branched-chain amino acid intake. Because BCKDK regulates BCKD which in turn catalyzes BCAA, BCKDK is one of the factors that determines the concentration of BCAA levels. High BCAA levels can lead to insulin resistance and can be a potential marker for type 2 diabetes. The amalgamation of BCAA can also lead to congenital heart diseases and heart failure. Furthermore, low levels of BCAA have been described as a cause of comorbid intellectual disability, autism, and epilepsy. Deficiency of BCKDK, first described in 2012, is a disorder that could be considered as the "opposite" of maple syrup disease, because patients have decreased levels of branched-chain amino acids, instead of increased levels. The condition may present as autism with epileptiform abnormalities on EEG and seizures.


Therapeutics development

In 2023, Pfizer reported the development of the thiophene PF-07208254 as an allosteric BCKDK inhibitor that also promotes BCKDK degradation by promoting BCKDK interaction with BCKDH-E2. A variant of this molecule, PF-07328948, was disclosed in 2024 and is being evaluated as a clinical candidate for heart failure.


Interactions

BCKDK has been seen to interact with: * BCKD


References


Further reading

* * * * * * *


External links

* * {{Portal bar, Biology, border=no EC 2.7.11