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Ribonuclease 4 is an 
RNase 4 features a unique structure compared to its homologous enzymes in the superfamily. It contains 119 amino acid residues making it the shortest known human RNase and contains no ''N-glycosylation'' sites. RNase 4 displays an α + β type polypeptide chain folding and a V-shape with the active site cleft in the middle. It contains three α-helices and four β -strands while the secondary structures are connected by six loops. There are four disulfide bridges located throughout the structure that connect the α-helices, β -strands, and loops. The overall structure of RNase 4 is similar to its homologous enzyme
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 ...
that in humans is encoded by the ''RNASE4'' 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 ...
.
Function
Theprotein
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 ...
encoded by this gene belongs to the pancreatic
The pancreas (plural pancreases, or pancreata) is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine ...
ribonuclease
Ribonuclease (commonly abbreviated RNase) is a type of nuclease that catalyzes the degradation of RNA into smaller components. Ribonucleases can be divided into endoribonucleases and exoribonucleases, and comprise several sub-classes within th ...
family. Secreted ribonucleases are the only enzyme family that is vertebrate-specific. Among the 13 members of this superfamily, ribonuclease 4 (RNase 4), is the most conserved gene across different vertebrate species. The human form of RNase 4 is an intracellular and plasma enzyme which was first isolated from colon adenocarcinoma cell line HT-29. It can be found in the pancreas, saliva, and the liver, displaying a similar distribution pattern to that of angiogenin (ANG). It plays an important role in mRNA
In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein.
mRNA is ...
cleavage and has marked specificity towards the 3' side of uridine nucleotides.
Alternative splicing
Alternative splicing, alternative RNA splicing, or differential splicing, is an alternative RNA splicing, splicing process during gene expression that allows a single gene to produce different splice variants. For example, some exons of a gene ma ...
results in two transcript variants encoding the same protein. RNase 4 is co-expressed and shares the same promoter with angiogenin (ANG), another member of this superfamily. Each gene splices to a unique downstream exon that contains its complete coding region. RNase 4 has also been studied in its involvement with amyotrophic lateral sclerosis (ALS), a nervous system disease, due to its similarity with ANG which has been associated with ALS pathogenesis.
Structure
RNase 4 features a unique structure compared to its homologous enzymes in the superfamily. It contains 119 amino acid residues making it the shortest known human RNase and contains no ''N-glycosylation'' sites. RNase 4 displays an α + β type polypeptide chain folding and a V-shape with the active site cleft in the middle. It contains three α-helices and four β -strands while the secondary structures are connected by six loops. There are four disulfide bridges located throughout the structure that connect the α-helices, β -strands, and loops. The overall structure of RNase 4 is similar to its homologous enzyme RNase A
Pancreatic ribonuclease family (, ''RNase'', ''RNase I'', ''RNase A'', ''pancreatic RNase'', ''ribonuclease I'', ''endoribonuclease I'', ''ribonucleic phosphatase'', ''alkaline ribonuclease'', ''ribonuclease'', ''gene S glycoproteins'', ''Cerati ...
, EDN, and angiogenin.
A shorter C terminus is a unique feature of RNase 4 which places the carboxy terminus in the pyrimidine recognition site which results in RNase 4 unique specificity. The pyrimidine recognition site is where there are major difference compared to its homologous enzymes. It contains an arginine residue at position 101, a phenylalanine reside at 42, and a threonine residue at 44. These residues contribute to the ribonuclease 4 specificity and are adapted to recognize a uridine-type base over cytidine-containing substrates.
References
Further reading
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