Ornithine aminotransferase

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ornithine aminotransferase
1gbn.jpg
OAT + PLP, Human
Identifiers
EC number 2.6.1.13
CAS number 9030-42-6
Databases
IntEnz IntEnz view
BRENDA BRENDA entry
ExPASy NiceZyme view
KEGG KEGG entry
MetaCyc metabolic pathway
PRIAM profile
PDB structures RCSB PDB PDBe PDBsum
Gene Ontology AmiGO / EGO
ornithine aminotransferase
Identifiers
Symbol OAT
Entrez 4942
HUGO 8091
OMIM 258870
RefSeq NM_000274
UniProt P04181
Other data
EC number 2.6.1.13
Locus Chr. 10 q26

Ornithine aminotransferase (OAT) is an enzyme which is encoded in human by the OAT gene located on chromosome 10.

The OAT involved in the ultimate formation of the non-essential amino acid proline from the amino acid ornithine. Ornithine aminotransferase forms the initial intermediate in this process. It catalyzes the reverse reaction as well, and is therefore essential in creating ornithine from the starting substrate proline.

Structure[edit]

The OAT gene encodes for a protein that is approximately 46 kDa in size. The OAT protein is expressed primarily in the liver and the kidney but also in the brain and the retina.[1] The OAT protein is localized to the mitochondrion within the cells where it is expressed.[2]

The structure of the OAT protein has been resolved usign X-ray cyrstallography and shows similarity to other subgroup 2 aminotransferases such as dialkyglucine decarboxylatse.[3] The OAT protein functions as a dimer and each monomer consists of a large domain, which contributes most to subunit interface, and a C-terminal small domain, and an N-terminal region containing a helix, loop, and three-sranded beta-meander. In the central large domain is a seven-stranded beta-sheet covered by eight helices. The co-factor of the OAT protein (pyridoxal-5'-phosphate) binds to OAT through a Schiff base at the lysine 292 position situated between two of the seven-stranded beta-sheet. Three amino acids (R 180, E 235, and R413) are thought to be involved in substrate binding at the active site.[3]

Function[edit]

Ornithine aminotransferase catalyzes the transfer of the delta-amino group from L-ornithine

  • L-ornithine + a 2-oxo acid = L-glutamate 5-semialdehyde + an L-amino acid

The reaction requires pyridoxal 5'-phosphate as a co-factor and forms part of the subpathway that synthesizes L-glutamate 5-semialdehyde from L-ornithine.

Clinical significance[edit]

Mutations in the OAT gene can lead to malfunctioning proteins, including both point mutations that abolish catalytic activities, large frame-shift mutations, as well as mutated proteins that are not properly targeted to the mitochondrion where its normal functionality occurs.[2] In the latter, abnormality of mitochondrial import causes ectopic accumulation of the OAT protein in the cytosol followed by rapid degradation by proteolysis. Deficiency of OAT activities causes ornithine aminotransferase deficiency, also known as gyrate atrophy of choroid and retina.[4][5][6][7]

The mechanism of gyrate atrophy of choroid and retina is thought to involve the toxicity of glyoxylate.[1]

See also[edit]

References[edit]

  1. ^ a b Rao GN, Cotlier E (1984). "Ornithine delta-aminotransferase activity in retina and other tissues". Neurochem. Res. 9 (4): 555–62. doi:10.1007/bf00964382. PMID 6462326. 
  2. ^ a b Kobayashi T, Ogawa H, Kasahara M, Shiozawa Z, Matsuzawa T (1995). "A single amino acid substitution within the mature sequence of ornithine aminotransferase obstructs mitochondrial entry of the precursor". Am. J. Hum. Genet. 57 (2): 284–91. PMC 1801533Freely accessible. PMID 7668253. 
  3. ^ a b Shen BW, Hennig M, Hohenester E, Jansonius JN, Schirmer T (1998). "Crystal structure of human recombinant ornithine aminotransferase". J. Mol. Biol. 277 (1): 81–102. doi:10.1006/jmbi.1997.1583. PMID 9514741. 
  4. ^ "Gyrate atrophy of the choroid and retina". National Institutes of Health. Retrieved 2012-08-23. 
  5. ^ Kim SJ, Lim DH, Kim JH, Kang SW (2013). "Gyrate atrophy of the choroid and retina diagnosed by ornithine-δ-aminotransferase gene analysis: a case report". Korean J Ophthalmol. 27 (5): 388–91. doi:10.3341/kjo.2013.27.5.388. PMC 3782588Freely accessible. PMID 24082780. 
  6. ^ Katagiri S, Gekka T, Hayashi T, Ida H, Ohashi T, Eto Y, Tsuneoka H (2014). "OAT mutations and clinical features in two Japanese brothers with gyrate atrophy of the choroid and retina". Doc Ophthalmol. 128 (2): 137–48. doi:10.1007/s10633-014-9426-1. PMID 24429551. 
  7. ^ Doimo M, Desbats MA, Baldoin MC, Lenzini E, Basso G, Murphy E, Graziano C, Seri M, Burlina A, Sartori G, Trevisson E, Salviati L (2013). "Functional analysis of missense mutations of OAT, causing gyrate atrophy of choroid and retina". Hum. Mutat. 34 (1): 229–36. doi:10.1002/humu.22233. PMID 23076989. 

External links[edit]