Pentraxins (PTX), also known as pentaxins, are an evolutionary conserved family of

proteins 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 ...

characterised by containing a pentraxin

protein domain In molecular biology, a protein domain is a region of a protein's polypeptide chain that is self-stabilizing and that folds independently from the rest. Each domain forms a compact folded three-dimensional structure. Many proteins consist of s ...

. Proteins of the pentraxin family are involved in acute immunological responses. They are a class of

pattern recognition receptor Pattern recognition receptors (PRRs) play a crucial role in the proper function of the innate immune system. PRRs are germline-encoded host sensors, which detect molecules typical for the pathogens. They are proteins expressed, mainly, by cells of ...

s (PRRs). They are a superfamily of multifunctional conserved proteins, some of which are components of the humoral arm of innate immunity and behave as functional ancestors of antibodies (Abs). They are known as classical acute phase proteins (APP), known for over a century.

Structure

Pentraxins are characterised by

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

dependent

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

binding and a distinctive flattened β-jellyroll structure similar to that of the

legume A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock f ...

lectins Lectins are carbohydrate-binding proteins that are highly specific for sugar groups that are part of other molecules, so cause agglutination of particular cells or precipitation of glycoconjugates and polysaccharides. Lectins have a role in rec ...

. The name "pentraxin" is derived from the Greek word for five (penta) and axle (axis) relating to the radial symmetry of five

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 Mo ...

s forming a ring approximately 95Å across and 35Å deep observed in the first members of this family to be identified. The "short" pentraxins include

Serum Amyloid P component The serum amyloid P component (SAP) is the identical serum form of amyloid P component (AP), a 25kDa pentameric protein first identified as the pentagonal constituent of in vivo pathological deposits called "amyloid". APCS is its human gene. In ...

(SAP) and

C reactive protein C-reactive protein (CRP) is an annular (ring-shaped) pentameric protein found in blood plasma, whose circulating concentrations rise in response to inflammation. It is an acute-phase protein of hepatic origin that increases following interleukin-6 ...

(CRP). The "long" pentraxins include

PTX3 Pentraxin-related protein PTX3 also known as TNF-inducible gene 14 protein (TSG-14) is a protein that in humans is encoded by the ''PTX3'' gene. Pentraxin 3 (ptx3) is a member of the pentraxin superfamily. This super family characterized by cycli ...

(a cytokine modulated molecule) and several neuronal pentraxins.

Family members

Three of the principal members of the pentraxin family are serum proteins: namely, C-reactive protein (CRP), serum amyloid P component protein (SAP), and female protein (FP).

(or TSG-14) protein is a cytokine-induced protein that is homologous to CRPs and SAPs, but its function has not yet been determined.

C-reactive protein

C-reactive protein C-reactive protein (CRP) is an annular (ring-shaped) pentameric protein found in blood plasma, whose circulating concentrations rise in response to inflammation. It is an acute-phase protein of hepatic origin that increases following interleukin-6 ...

is expressed during acute phase response to tissue injury or inflammation in mammals. The protein resembles antibody and performs several functions associated with host defence: it promotes agglutination, bacterial capsular swelling and phagocytosis, and activates the classical complement pathway through its calcium-dependent binding to phosphocholine. CRPs have also been sequenced in an invertebrate, ''

Limulus polyphemus The Atlantic horseshoe crab (''Limulus polyphemus''), also known as the American horseshoe crab, is a species of marine and brackish chelicerate arthropod. Despite their name, horseshoe crabs are more closely related to spiders, ticks, and scorpi ...

'' (Atlantic horseshoe crab), where they are a normal constituent of the hemolymph.

Pentraxin 3

Pentraxin 3 (PTX3) is an acute phase protein whose levels rise during severe infections in humans. In case of central nervous system infections PTX3 helps distinguishes between bacterial and aseptic meningoencephalitis. It is significantly higher in bacterial meningoencephalitis.

Serum amyloid P component

Serum amyloid P component The serum amyloid P component (SAP) is the identical serum form of amyloid P component (AP), a 25kDa pentameric protein first identified as the pentagonal constituent of in vivo pathological deposits called "amyloid". APCS is its human gene. In ...

is a vertebrate protein that is identical to tissue forms of amyloid P component. It is found in all types of amyloid deposits, in glomerular basement membrane and in elastic fibres in blood vessels. SAP binds to various lipoprotein ligands in a calcium-dependent manner, and it has been suggested that, in mammals, this may have important implications in atherosclerosis and amyloidosis.

Hamster female protein

Hamster female protein is a SAP homologue found in ''

Mesocricetus auratus The golden hamster or Syrian hamster (''Mesocricetus auratus'') is a rodent belonging to the hamster subfamily, Cricetinae. Their natural geographical range is in an arid region of northern Syria and southern Turkey. Their numbers have been de ...

'' (Golden hamster). The concentration of this plasma protein is altered by sex steroids and stimuli that elicit an acute phase response.

Nervous system

Pentraxin proteins expressed in the nervous system are neural pentraxin I ( NPTXI) and II ( NPTXII). NPTXI and NPTXII are homologous and can exist within one species. It is suggested that both proteins mediate the uptake of synaptic macromolecules and play a role in synaptic plasticity. Apexin, a sperm acrosomal protein, is a homologue of NPTXII found in ''

Cavia porcellus The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy (), is a species of rodent belonging to the genus ''Cavia'' in the family Caviidae. Breeders tend to use the word ''cavy'' to describe the ani ...

'' (Guinea pig).

Human

Human genes encoding proteins that contain this domain include: * APCS * CRP *

GPR144 Probable G-protein coupled receptor 144 is a protein that in humans is encoded by the ''GPR144'' gene. This gene encodes a member of the adhesion-GPCR family of receptors. Family members are characterised by an extended extracellular region with ...

NPTX1 Neuronal pentraxin-1 (NP1) is a protein that in humans is encoded by the ''NPTX1'' gene. Function NPTX1 is a member of the neuronal pentraxin Pentraxins (PTX), also known as pentaxins, are an evolutionary conserved family of proteins cha ...

;

NPTX2 Neuronal pentraxin-2 is a protein that in humans is encoded by the ''NPTX2'' gene. Function This gene encodes a member of the family of neuronal pentraxins, synaptic proteins that are related to C-reactive protein. This protein is involved in e ...

;

NPTXR Neuronal pentraxin receptor is a protein that in humans is encoded by the ''NPTXR'' gene. This gene encodes a protein similar to the rat neuronal pentraxin receptor. The rat protein pentraxin is thought to mediate neuronal uptake of synaptic mater ...

* SVEP1

References

{{InterPro content, IPR001759 Protein families Protein domains Single-pass transmembrane proteins