DnaB helicase
Encyclopedia
dnaB helicase is an enzyme in bacteria
which opens the replication fork
during DNA replication
. Although the mechanism by which DnaB both couples ATP hydrolysis
to translocation along DNA
and denatures the duplex is unknown, a change in the quaternary structure of the protein
involving dimerisation
of the N-terminal domain
has been observed and may occur during the enzymatic
cycle. Initially when DnaB binds to dnaA
, it is associated with dnaC
, a negative regulator. After DnaC dissociates, DnaB binds dnaG
.
The N-terminal has a multi-helical structure that forms an orthogonal bundle. The C-terminal domain contains an ATP
-binding site and is therefore probably the site of ATP hydrolysis.
In eukaryotes, helicase function is provided by the T antigen.
The DnaB helicase is the product of the dnaB gene. The helicase enzyme that is produced is a hexamer in E. coli, as well as in many other bacteria.
The energy for DnaB activity is provided by NTP hydrolysis. Mechanical energy moves the DnaB into the replication fork, physically splitting it in half.
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
which opens the replication fork
Replication fork
The replication fork is a structure that forms within the nucleus during DNA replication. It is created by helicases, which break the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA...
during DNA replication
DNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
. Although the mechanism by which DnaB both couples ATP hydrolysis
ATP hydrolysis
ATP hydrolysis is the reaction by which chemical energy that has been stored and transported in the high-energy phosphoanhydridic bonds in ATP is released, for example in the muscles, to produce work. The product is ADP and an inorganic phosphate, orthophosphate...
to translocation along DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
and denatures the duplex is unknown, a change in the quaternary structure of the protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
involving dimerisation
Protein dimer
In biochemistry, a dimer is a macromolecular complex formed by two, usually non-covalently bound, macromolecules like proteins or nucleic acids...
of the N-terminal domain
Protein domain
A protein domain is a part of protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Many proteins consist of several structural...
has been observed and may occur during the enzymatic
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
cycle. Initially when DnaB binds to dnaA
DnaA
dnaA is a replication initiation factor which promotes the unwinding or denaturation of DNA at oriC , during DNA replication in prokaryotes....
, it is associated with dnaC
DnaC
dnaC is a bacterial gene that codes for protein DnaC. DnaC, also known as the helicase loader, is a regulator of DnaB. DnaC forms a complex with DnaB, thus enabling DnaB to perform its functions in bacterial DNA replication. This interaction of DnaC with DnaB requires the hydrolysis of ATP....
, a negative regulator. After DnaC dissociates, DnaB binds dnaG
DnaG
DnaG is a bacterial primase which synthesizes short RNA oligonucleotides during DNA replication. These RNA oligonucleotides serve as primers for DNA synthesis by bacterial DNA polymerase Pol III. On one of the two parental strands, called the lagging strand, the primase makes a primer every few...
.
The N-terminal has a multi-helical structure that forms an orthogonal bundle. The C-terminal domain contains an ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
-binding site and is therefore probably the site of ATP hydrolysis.
In eukaryotes, helicase function is provided by the T antigen.
The DnaB helicase is the product of the dnaB gene. The helicase enzyme that is produced is a hexamer in E. coli, as well as in many other bacteria.
The energy for DnaB activity is provided by NTP hydrolysis. Mechanical energy moves the DnaB into the replication fork, physically splitting it in half.