Hin recombinase
Encyclopedia
Hin recombinase is a 21kD protein
composed of 198 amino acid
s that is found in the bacteria Salmonella
. Hin belongs to the serine recombinase family of DNA invertases in which it relies on the active site
serine
to initiate DNA cleavage and recombination. The related protein, gamma-delta resolvase shares high similarity to Hin, of which much structural work has been done, including structures bound to DNA and reaction intermediate
s. Hin functions to invert a 900 base pair (bp
) DNA segment within the salmonella genome
that contains a promoter for downstream flagellar genes, fljA and fljB. Inversion of the intervening DNA alternates the direction of the promoter and thereby alternates expression
of the flagellar genes. This is advantageous to the bacterium as a means of escape from the host
immune response.
Hin functions by binding to two 26bp imperfect inverted repeat sequences as a homodimer. These hin binding sites flank the invertible segment which not only encodes the Hin gene itself, but also contains an enhancer element to which the bacterial Fis
proteins binds with nanomolar affinity. Four molecules of Fis bind to this site as a homodimers and are required for the recombination reaction to proceeded.
The initial reaction requires binding of Hin and Fis to their respective DNA sequences and assemble into a higher-order nucleoprotein
complex with branched plectonemic supercoils with the aid of the DNA bending protein HU. At this point, it is believed that the Fis protein modulates subtle contacts to activate the reaction, possibly through direct interactions with the Hin protein. Activation of the 4 catalytic serine residues within the Hin tetramer make a 2-bp double stranded DNA break and forms a covalent reaction intermediate. The DNA cleavage event also requires the divalent metal cation magnesium
. A large conformational change
reveals a large hydrophobic interface that allows for subunit rotation which may be driven by superhelical torsion within the protein-DNA complex. After this 180° rotation, Hin returns to its native conformation and re-ligates the cleaved DNA, without the aid of high energy cofactors and without the loss of any DNA.
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...
composed of 198 amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s that is found in the bacteria Salmonella
Salmonella
Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...
. Hin belongs to the serine recombinase family of DNA invertases in which it relies on the active site
Active site
In biology the active site is part of an enzyme where substrates bind and undergo a chemical reaction. The majority of enzymes are proteins but RNA enzymes called ribozymes also exist. The active site of an enzyme is usually found in a cleft or pocket that is lined by amino acid residues that...
serine
Serine
Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...
to initiate DNA cleavage and recombination. The related protein, gamma-delta resolvase shares high similarity to Hin, of which much structural work has been done, including structures bound to DNA and reaction intermediate
Reaction intermediate
A reaction intermediate or an intermediate is a molecular entity that is formed from the reactants and reacts further to give the directly observed products of a chemical reaction. Most chemical reactions are stepwise, that is they take more than one elementary step to complete...
s. Hin functions to invert a 900 base pair (bp
Base pair
In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...
) DNA segment within the salmonella genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
that contains a promoter for downstream flagellar genes, fljA and fljB. Inversion of the intervening DNA alternates the direction of the promoter and thereby alternates expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...
of the flagellar genes. This is advantageous to the bacterium as a means of escape from the host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
immune response.
Hin functions by binding to two 26bp imperfect inverted repeat sequences as a homodimer. These hin binding sites flank the invertible segment which not only encodes the Hin gene itself, but also contains an enhancer element to which the bacterial Fis
FIS (protein)
FIS is a nucleoid-associated protein in E. coli. It is highly expressed from fis gene from the end of the stationary phase till the mid-exponential phase. It is a DNA binding protein. It affects the topology and supercoiling of E. coli chromosome, and it regulates the expression of many other...
proteins binds with nanomolar affinity. Four molecules of Fis bind to this site as a homodimers and are required for the recombination reaction to proceeded.
The initial reaction requires binding of Hin and Fis to their respective DNA sequences and assemble into a higher-order nucleoprotein
Nucleoprotein
A nucleoprotein is any protein that is structurally associated with nucleic acid .Many viruses harness this protein, and they are known for being host-specific...
complex with branched plectonemic supercoils with the aid of the DNA bending protein HU. At this point, it is believed that the Fis protein modulates subtle contacts to activate the reaction, possibly through direct interactions with the Hin protein. Activation of the 4 catalytic serine residues within the Hin tetramer make a 2-bp double stranded DNA break and forms a covalent reaction intermediate. The DNA cleavage event also requires the divalent metal cation magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
. A large conformational change
Conformational change
A macromolecule is usually flexible and dynamic. It can change its shape in response to changes in its environment or other factors; each possible shape is called a conformation, and a transition between them is called a conformational change...
reveals a large hydrophobic interface that allows for subunit rotation which may be driven by superhelical torsion within the protein-DNA complex. After this 180° rotation, Hin returns to its native conformation and re-ligates the cleaved DNA, without the aid of high energy cofactors and without the loss of any DNA.