The tailspike protein (P22TSP) of Enterobacteria phage P22 mediates the recognition and adhesion between the bacteriophage and the surface of ''

Salmonella enterica ''Salmonella enterica'' (formerly ''Salmonella choleraesuis'') is a rod-headed, flagellate, facultative anaerobic, Gram-negative bacterium and a species of the genus ''Salmonella''. A number of its serovars are serious human pathogens. Epidemi ...

'' cells. It is anchored within the viral coat and recognizes the O-antigen portion of the

lipopolysaccharide Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the outer ...

(LPS) on the outer-membrane of

Gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

. It possesses endoglycanase activity, serving to shorten the length of the O-antigen during infection.

History

The initial interest in tailspike proteins was in the study of the effect the mutations on

protein folding Protein folding is the physical process by which a protein chain is translated to its native three-dimensional structure, typically a "folded" conformation by which the protein becomes biologically functional. Via an expeditious and reproduc ...

. Some mutations affect the folding efficiency of the protein but have no effect on the final

native Native may refer to: People * Jus soli, citizenship by right of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Native Americans (disambiguation) In arts and entert ...

structure. Other mutations have been identified that lead to a temperature sensitive phenotype. Reconstitution experiments have demonstrated that the

in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called " test-tube experiments", these studies in biology ...

folding Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure * Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Abov ...

process closely mirrors the

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...

pathway. It has been further been demonstrated that folding yields in vitro decrease strongly with increasing temperature.

Function

O-antigen binding

P22TSP recognizes the O-antigen polysaccharide of LPS serotypes A, B, or D1. The serotypes correspond to species ''S. Typhimurium'', ''S. Enteritidis'', and ''S. Paratyphi A''. These

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or m ...

s share the same main chain trisaccharide repeating unit alpha-D-

mannose Mannose is a sugar monomer of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation of certain proteins. Several congenital disorders of glycosylation ...

-(1—4)-alpha-L- rhamnose-(1—3)-alpha-D-

galactose Galactose (, '' galacto-'' + ''-ose'', "milk sugar"), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epimer of glucose. A galactose molecu ...

-(1—2), but each have a different 2,6-dideoxyhexose substituent at C-3 of the

In vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...

, P22TSP binds as a homotrimer and one

phage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacter ...

particle can carry up to 6 tailspikes. P22TSP can bind multivalently, leading to an essentially irreversible attachment. It was shown that a minimum of two repeating units or an octasaccharide is required for binding. The TSP is also capable of binding longer fragments with similar affinity.

Endoglycosidase activity

P22TSP has endorhamnosidase activity and cleaves the

glycosidic bond A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. A glycosidic bond is formed between the hemiacetal or hemiketal group ...

of the rhamnose group, producing an octasaccharide product. Two aspartic acids and one glutamic acid in the active site have been strongly linked to

enzymatic activity Enzyme assays are laboratory methods for measuring enzymatic activity. They are vital for the study of enzyme kinetics and enzyme inhibition. Enzyme units The quantity or concentration of an enzyme can be expressed in molar amounts, as with an ...

. Different biological functions for this cleavage have been proposed. Cleavage could facilitate access to the

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...

. or allow the

to find the optimal position for

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dis ...

Role in DNA injection

It has been demonstrated that cleavage of the O-antigen is necessary for DNA ejection by the

. It has been proposed that P22TSP binding positions the

to inject its DNA.

Structure

P22TSP is a homotrimeric structural protein consisting of 666

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 a ...

s. It is noncovalently bound to the neck of the viral

capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or ma ...

. It has been crystallized in

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...

P213 and has one

monomer In chemistry, a monomer ( ; '' mono-'', "one" + ''-mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization. Classification ...

in the asymmetric unit. The secondary structure of P22TSP is dominated by a parallel

Beta helix A beta helix is a tandem protein repeat structure formed by the association of parallel beta strands in a helical pattern with either two or three faces. The beta helix is a type of solenoid protein domain. The structure is stabilized by inter- ...

comprising 13 complete turns. This structure is further characterized as a beta-solenoid domain. P22TSP is compOsed of two domains, each with distinct function. An N-terminal domains serves to bind to the

particle and a

C-terminal The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...

domains that interacts with the '' Salmonella'' surface. These two domains are connected by a flexible linker. The

binding site In biochemistry and molecular biology, a binding site is a region on a macromolecule such as a protein that binds to another molecule with specificity. The binding partner of the macromolecule is often referred to as a ligand. Ligands may includ ...

of P22TSP is located in the central part of the

. A deep cleft is formed by a 60-

residue Residue may refer to: Chemistry and biology * An amino acid, within a peptide chain * Crop residue, materials left after agricultural processes * Pesticide residue, refers to the pesticides that may remain on or in food after they are applied ...

insertion on one side along with three smaller 5-25

insertions on the other.

Homologous proteins

Several functional homologues of P22TSP has been identified belonging to the bacteriophages HK620 and Sf6. Both of these tailspike

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, res ...

s also contain right-handed parallel beta-helices and share similar O-antigen binding and cleavage to P22TSP. These proteins share 70%

sequence identity In bioinformatics, a sequence alignment is a way of arranging the sequences of DNA, RNA, or protein to identify regions of similarity that may be a consequence of functional, structural, or evolutionary relationships between the sequences. Ali ...

in their N-terminal domains, but no

sequence similarities Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a s ...

have been found in the

domains.

Translational applications

Carbohydrate binding scaffolds

P22TSP has also been studied due to its high kinetic stability. As it exists and functions in the

extracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

environment, it must endure harsh conditions such as highly variable temperatures or high concentrations of protein degrading

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 ...

s. The kinetic stability of P22TSP derives from its compact beta-solenoid architecture. It was shown that like other viral fibrous proteins, P22 tailspike protein possesses a high stability against denaturation. This makes P22TSP a promising candidate for use as thermostable scaffold capable of being tailor-made to recognize heteropolymers.

Therapy against ''Salmonella'' infection

Tailspike proteins have also shown potential for more translational applications such as fighting

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

s. A study has demonstrated that orally administered P22TSP markedly reduced '' Salmonella'' colonization in a group of chickens. They suggest that the endorhamnosidase activity of the free tailspike molecule serves to modify O-antigen, compromising the LPS structure and thereby preventing the binding of a phage P22-attached tailspike protein. The authors suggest that this has the potential to be a novel therapy meant to fight

References

{{Reflist, 33em Proteins