The enzyme polynucleotide 5′-phosphatase (RNA 5′-triphosphatase, RTPase, EC 3.1.3.33) is an
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
that
catalyzes the reaction
:a 5′-phosphopolynucleotide + H
2O
a polynucleotide + phosphate
This enzyme belongs to the family of
hydrolase
Hydrolase is a class of enzyme that commonly perform as biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules. Some common examples of hydrolase enzymes are este ...
s, specifically those acting on phosphoric
monoester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are fa ...
bonds. The
systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature.
A semisystematic name or semitrivial ...
is polynucleotide 5′-phosphohydrolase. This enzyme is also called 5′-polynucleotidase.
The only specific molecular function known is the catalysis of the reaction:
:a 5′-end triphospho-(purine-ribonucleotide) in mRNA + H
2O = a 5′-end diphospho-(purine-ribonucleoside) in mRNA + phosphate
RTPases cleave the 5′-terminal γ-β phosphoanhydride bond of nascent
messenger RNA
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 synthesizing a protein.
mRNA is created during the p ...
molecules, enabling the addition of a
five-prime cap
In molecular biology, the five-prime cap (5′ cap) is a specially altered nucleotide on the 5′ end of some primary transcripts such as precursor messenger RNA. This process, known as mRNA capping, is highly regulated and vital in the creation o ...
as part of
post-transcriptional modification
Transcriptional modification or co-transcriptional modification is a set of biological processes common to most eukaryotic cells by which an RNA primary transcript is chemically altered following transcription from a gene to produce a mature, func ...
s. RTPases generate 5′-diphosphate-ended mRNA and a phosphate ion from 5′-triphosphate-ended
precursor mRNA
Precursor or Precursors may refer to:
*Precursor (religion), a forerunner, predecessor
** The Precursor, John the Baptist
Science and technology
* Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of unr ...
.
mRNA guanylyltransferase
In enzymology, a mRNA guanylyltransferase () is an enzyme that catalyzes the chemical reaction
:GTP + (5')ppPur-mRNA \rightleftharpoons diphosphate + G(5')pppPur-mRNA
Thus, the two substrates of this enzyme are GTP and (5')ppPur-mRNA, where ...
then adds a backwards
guanosine monophosphate
Guanosine monophosphate (GMP), also known as 5′-guanidylic acid or guanylic acid (conjugate base guanylate), is a nucleotide that is used as a monomer in RNA. It is an ester of phosphoric acid with the nucleoside guanosine. GMP consists of the ...
(GMP) group from
GTP, generating
pyrophosphate
In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a P–O–P linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate (Na2H2P2O7) and tetrasodium pyrophosphate (Na4P2O7), among other ...
, and
mRNA (guanine-N7-)-methyltransferase
In enzymology, a mRNA (guanine-N7-)-methyltransferase also known as mRNA cap guanine-N7 methyltransferase is an enzyme that catalyzes the chemical reaction
:''S''-adenosyl-L-methionine + G(5')pppR-RNA \rightleftharpoons ''S''-adenosyl-L-homocys ...
methylates the
guanine
Guanine () ( symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is called ...
to form the final 5′-cap structure.
There are two families of RTPases known so far:
*the metal-dependent family.
Yeast
Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...
,
protozoa
Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
n, and viral RTPases require a metal co-factor for their activity, which is most often either Mg2+ or Mn2+. This class of enzymes is also able to hydrolyze free nucleoside triphosphate
A nucleoside triphosphate is a nucleoside containing a nitrogenous base bound to a 5-carbon sugar (either ribose or deoxyribose), with three phosphate groups bound to the sugar. They are the molecular precursors of both DNA and RNA, which are cha ...
s in the presence of either Mn2+ or Co2+.[
*the metal-independent family. These groups do not require metals for their activity, and some enzymes have been shown to be inactivated in the presence of metal ions. These enzymes are very much similar to ]protein tyrosine phosphatase
Protein tyrosine phosphatases (EC 3.1.3.48, systematic name protein-tyrosine-phosphate phosphohydrolase) are a group of enzymes that remove phosphate groups from phosphorylated tyrosine residues on proteins:
: proteintyrosine phosphate + H2O = ...
s in their structure and mechanism. This family includes RTPases from mammals, plants, and other higher eukaryotes,[ and is structurally and mechanistically different from the metal-dependent RTPase family.][
]
Structural studies
As of late 2007, 5 structures
A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...
have been solved for this class of enzymes, with PDB accession codes , , , , and .
See also
* Transcription (genetics)
Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode proteins are said to produce messenger RNA (mRNA). Other segments of DNA are copied into RNA molecules called ...
* Five-prime cap
In molecular biology, the five-prime cap (5′ cap) is a specially altered nucleotide on the 5′ end of some primary transcripts such as precursor messenger RNA. This process, known as mRNA capping, is highly regulated and vital in the creation o ...
References
Further reading
*
EC 3.1.3
Enzymes of known structure
{{3.1-enzyme-stub