Hin recombinase is a 21kD

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

composed of 198

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

s that is found in the bacteria ''

Salmonella ''Salmonella'' is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' is the type species and is fur ...

''. Hin belongs to the serine recombinase family (B2) of DNA invertases in which it relies on the

active site In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate (binding site) a ...

serine Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − form un ...

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 In chemistry, a reaction intermediate or an intermediate is a molecular entity that is formed from the reactants (or preceding intermediates) but is consumed in further reactions in stepwise chemical reactions that contain multiple elementary st ...

s. Hin functions to invert a 900 base pair ( bp) DNA segment within the salmonella

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

that contains a promoter for

downstream Downstream may refer to: * Downstream (bioprocess) * Downstream (manufacturing) * Downstream (networking) * Downstream (software development) * Downstream (petroleum industry) * Upstream and downstream (DNA), determining relative positions on DNA ...

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

r genes, fljA and fljB. Inversion of the intervening DNA alternates the direction of the promoter and thereby alternates

expression Expression may refer to: Linguistics * Expression (linguistics), a word, phrase, or sentence * Fixed expression, a form of words with a specific meaning * Idiom, a type of fixed expression * Metaphorical expression, a particular word, phrase, o ...

of the flagellar genes. This is advantageous to the bacterium as a means of escape from the

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman * Michel Host ...

immune response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of different microorganisms including viruses, bacteria, parasites, and fungi which could ...

. Hin functions by binding to two 26bp imperfect inverted repeat sequences as a

homodimer In biochemistry, a protein dimer is a macromolecular complex formed by two protein monomers, or single proteins, which are usually non-covalently bound. Many macromolecules, such as proteins or nucleic acids, form dimers. The word ''dimer'' ha ...

. 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 or fis may refer to: Science and technology * '' Fis'', an ''E. Coli'' gene * Fis phenomenon, a phenomenon in linguistics * F♯ (musical note) * Flight information service, an air traffic control service * Frame Information Structure, a Se ...

proteins binds with nanomolar affinity. Four molecules of Fis bind to this site as a homodimers and are required for the recombination reaction to proceed. The initial reaction requires binding of Hin and Fis to their respective DNA sequences and assemble into a higher-order

nucleoprotein Nucleoproteins are proteins conjugated with nucleic acids (either DNA or RNA). Typical nucleoproteins include ribosomes, nucleosomes and viral nucleocapsid proteins. Structures Nucleoproteins tend to be positively charged, facilitating int ...

complex with branched plectonemic

supercoil DNA supercoiling refers to the amount of twist in a particular DNA strand, which determines the amount of strain on it. A given strand may be "positively supercoiled" or "negatively supercoiled" (more or less tightly wound). The amount of a st ...

s 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 A tetramer () (''tetra-'', "four" + '' -mer'', "parts") is an oligomer formed from four monomers or subunits. The associated property is called ''tetramery''. An example from inorganic chemistry is titanium methoxide with the empirical formula Ti ...

make a 2-bp double stranded DNA break and forms a covalent reaction intermediate. The DNA cleavage event also requires the divalent metal

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

. A large

conformational change In biochemistry, a conformational change is a change in the shape of a macromolecule, often induced by environmental factors. A macromolecule is usually flexible and dynamic. Its shape can change in response to changes in its environment or oth ...

reveals a large

hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, th ...

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.

References

* * * * {{cite journal , vauthors=Li W, Kamtekar S, Xiong Y, Sarkis G, Grindley N, Steitz T , title=Structure of a synaptic gammadelta resolvase tetramer covalently linked to two cleaved DNAs , journal=Science , volume=309 , issue=5738 , pages=1210–5 , year=2005 , pmid=15994378 , doi=10.1126/science.1112064, bibcode=2005Sci...309.1210L , s2cid=84409916 Genetics techniques Molecular biology