Proteinase-activated receptor 1

Last updated
F2R
PDB 1nrn EBI.jpg
Available structures
PDB Ortholog search: PDBe RCSB
Identifiers
Aliases F2R , CHTR, PAR-1, PAR1, TR, Coagulation factor II receptor, coagulation factor II thrombin receptor
External IDs OMIM: 187930 MGI: 101802 HomoloGene: 1510 GeneCards: F2R
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_001992
NM_001311313

NM_010169

RefSeq (protein)

NP_001298242
NP_001983

NP_034299

Location (UCSC) Chr 5: 76.72 – 76.74 Mb Chr 13: 95.74 – 95.75 Mb
PubMed search [3] [4]
Wikidata
View/Edit Human View/Edit Mouse

Proteinase-activated receptor 1 (PAR1) also known as protease-activated receptor 1, coagulation factor II receptor and thrombin receptor is a protein that in humans is encoded by the F2R gene. [5] PAR1 is a G protein-coupled receptor and one of four protease-activated receptors involved in the regulation of thrombotic response. Highly expressed in platelets and endothelial cells, PAR1 plays a key role in mediating the interplay between coagulation and inflammation, which is important in the pathogenesis of inflammatory and fibrotic lung diseases. [6] It is also involved both in disruption and maintenance of endothelial barrier integrity, through interaction with either thrombin or activated protein C, respectively. [7]

Structure

PAR1 is a transmembrane G-protein-coupled receptor (GPCR) that shares much of its structure with the other protease-activated receptors. [8] [9] These characteristics include having seven transmembrane alpha helices, four extracellular loops and three intracellular loops. [9] PAR1 specifically contains 425 amino acid residues arranged for optimal binding of thrombin at its extracellular N-terminus. The C-terminus of PAR1 is located on the intracellular side of the cell membrane as part of its cytoplasmic tail. [8]

Signal transduction pathway

This image gives an overview of the cleavage of PAR1 by thrombin. Thrombin, in red, binds to the cleavage site at the extracellular N-terminus of PAR1. Thrombin cleaves the peptide bond between Arg-41 and Ser-42 to reveal a tethered ligand at the new N-terminus and the cleaved peptide, in orange, is released outside of the cell. PAR1 Cleavage.png
This image gives an overview of the cleavage of PAR1 by thrombin. Thrombin, in red, binds to the cleavage site at the extracellular N-terminus of PAR1. Thrombin cleaves the peptide bond between Arg-41 and Ser-42 to reveal a tethered ligand at the new N-terminus and the cleaved peptide, in orange, is released outside of the cell.

Activation

PAR1 is activated when the terminal 41 amino acids of its N-terminus are cleaved by thrombin, a serine protease. [10] Thrombin recognizes PAR1 by a Lysine-Aspartate-Proline-Arginine-Serine sequence at the N-terminal, where it cuts the peptide bond between Arginine-41 and Serine-42. The affinity of thrombin to this specific cleavage site in PAR1 is further aided by secondary interactions between thrombin's exosite and an acidic region of amino acid residues located C-terminal to Ser-42. [11] This proteolytic cleavage is irreversible and the loose peptide, often referred to as parstatin, is then released outside of the cell. [10] The newly revealed N-terminus acts as a tethered ligand that binds to a binding region between extracellular loops 3 and 4 of PAR1, therefore activating the protein. The binding instigates conformational changes in the protein that ultimately allow for the binding of G-proteins to sites on the intracellular region of PAR1. [12]

Signalling

Once cleaved, PAR1 can activate G-proteins that bind to several locations on its intracellular loops. For example, PAR1 in conjunction with PAR4 can couple to and activate G-protein G12/13 which in turn activates Rho and Rho kinase. [8] This pathway leads to the quick alteration of platelet shape due to actin contractions that lead to platelet mobility, as well as the release of granules which are both necessary for platelet aggregation. [8] Coupling can also occur with Gq, leading to phospholipase C-β activation; this pathway results in the stimulation of protein kinase C (PKC) which impacts platelet activation. [8]

Additionally, both PAR1 and PAR4 can couple to G-protein q which stimulates intracellular movement for Calcium ions that serve as second messengers for platelet activation. [8] This also activates protein kinase C which stimulates platelet aggregation and therefore blood coagulation further down the pathway. [11]

Termination

The phosphorylation of PAR1's cytoplasmic tail and subsequent binding to arrestin uncouples the protein from G protein signaling. [10] [11] These phosphorylated PAR1s are transported back into the cell via endosomes where they are sent to Golgi bodies. The cleaved PAR1s are then sorted and transported to lysosomes where they are degraded. [11] This internalization and degradation process is necessary for the termination of receptor signaling. [10]

In order to regain thrombin responsiveness, PAR1 must be replenished in the cell surface. Uncleaved PAR1 in the cell membrane gets bound by the AP2 adaptor complex at a tyrosine motif on the intracellular C-terminus, which stimulates the endocytosis of the unactivated PAR1. [13] It is then stored in clathrin-coated vesicles within the cytosol and ultimately protected from proteolysis. This ensures that there is a constant supply of uncleaved PAR1 that can be cycled into the plasma membrane independent of PAR1 reproduction, thus resensitizing the cell to thrombin and resetting the signal transduction pathway. [14]

This is a rendering of PAR1's structure when bound to an antagonist, Vorapaxar. The light blue structures represent the seven transmembrane alpha helices of PAR1. The green structures represent the extracellular loops and the orange structures represent the intracellular loops. The red molecule is Vorapaxar. C-terminal tail not pictured. PAR1 Vorapaxar 3.jpg
This is a rendering of PAR1's structure when bound to an antagonist, Vorapaxar. The light blue structures represent the seven transmembrane alpha helices of PAR1. The green structures represent the extracellular loops and the orange structures represent the intracellular loops. The red molecule is Vorapaxar. C-terminal tail not pictured.

Ligands

Agonists

Finding selective agonists for PAR1 has also been a topic of interest for researchers. A synthetic SFLLRN peptide has been found to serve as an agonist for PAR1. The SFLLRN peptide mimics the first six residues of the N-terminal tethered ligand of activated PAR1 and binds to the same binding site on the second extracellular loop. [15] So, even in the absence of thrombin, SFLLRN binding can garner a response from cleaved or uncleaved PAR1. [16]

Antagonists

Selective antagonists for the PAR1 receptor have been developed for use as anti-clotting agents.

See also

Related Research Articles

<span class="mw-page-title-main">G protein-coupled receptor</span> Class of cell surface receptors coupled to G-protein-associated intracellular signaling

G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily related proteins that are cell surface receptors that detect molecules outside the cell and activate cellular responses. They are coupled with G proteins. They pass through the cell membrane seven times in the form of six loops of amino acid residues, which is why they are sometimes referred to as seven-transmembrane receptors. Ligands can bind either to the extracellular N-terminus and loops or to the binding site within transmembrane helices. They are all activated by agonists, although a spontaneous auto-activation of an empty receptor has also been observed.

<span class="mw-page-title-main">Proteolysis</span> Breakdown of proteins into smaller polypeptides or amino acids

Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called proteases, but may also occur by intra-molecular digestion.

<span class="mw-page-title-main">Signal transduction</span> Cascade of intracellular and molecular events for transmission/amplification of signals

Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events. Most commonly, protein phosphorylation is catalyzed by protein kinases, ultimately resulting in a cellular response. Proteins responsible for detecting stimuli are generally termed receptors, although in some cases the term sensor is used. The changes elicited by ligand binding in a receptor give rise to a biochemical cascade, which is a chain of biochemical events known as a signaling pathway.

<span class="mw-page-title-main">Thrombin</span> Enzyme involved in blood coagulation in humans

Prothrombin is encoded in the human by the F2 gene. It is proteolytically cleaved during the clotting process by the prothrombinase enzyme complex to form thrombin.

<span class="mw-page-title-main">Serpin</span> Superfamily of proteins with similar structures and diverse functions

Serpins are a superfamily of proteins with similar structures that were first identified for their protease inhibition activity and are found in all kingdoms of life. The acronym serpin was originally coined because the first serpins to be identified act on chymotrypsin-like serine proteases. They are notable for their unusual mechanism of action, in which they irreversibly inhibit their target protease by undergoing a large conformational change to disrupt the target's active site. This contrasts with the more common competitive mechanism for protease inhibitors that bind to and block access to the protease active site.

Protease-activated receptors (PAR) are a subfamily of related G protein-coupled receptors that are activated by cleavage of part of their extracellular domain. They are highly expressed in platelets, and also on endothelial cells, fibroblasts, immune cells, myocytes, neurons, and tissues that line the gastrointestinal tract.

<span class="mw-page-title-main">Plasminogen activator</span> Type of protein

Plasminogen activators are serine proteases that catalyze the activation of plasmin via proteolytic cleavage of its zymogen form plasminogen. Plasmin is an important factor in fibrinolysis, the breakdown of fibrin polymers formed during blood clotting. There are two main plasminogen activators: urokinase (uPA) and tissue plasminogen activator (tPA). Tissue plasminogen activators are used to treat medical conditions related to blood clotting including embolic or thrombotic stroke, myocardial infarction, and pulmonary embolism.

<span class="mw-page-title-main">P-selectin</span> Type-1 transmembrane protein

P-selectin is a type-1 transmembrane protein that in humans is encoded by the SELP gene.

In biology, cell signaling is the process by which a cell interacts with itself, other cells, and the environment. Cell signaling is a fundamental property of all cellular life in prokaryotes and eukaryotes.

<span class="mw-page-title-main">Cathepsin S</span> Protein-coding gene in the species Homo sapiens

Cathepsin S is a protein that in humans is encoded by the CTSS gene. Transcript variants utilizing alternative polyadenylation signals exist for this gene.

<span class="mw-page-title-main">Thrombin receptor</span>

There are three known thrombin receptors (ThrR), termed PAR1, PAR3 and PAR4.

<span class="mw-page-title-main">Cathepsin G</span> Protein-coding gene in the species Homo sapiens

Cathepsin G is a protein that in humans is encoded by the CTSG gene. It is one of the three serine proteases of the chymotrypsin family that are stored in the azurophil granules, and also a member of the peptidase S1 protein family. Cathepsin G plays an important role in eliminating intracellular pathogens and breaking down tissues at inflammatory sites, as well as in anti-inflammatory response.

<span class="mw-page-title-main">LRP1</span> Mammalian protein found in Homo sapiens

Low density lipoprotein receptor-related protein 1 (LRP1), also known as alpha-2-macroglobulin receptor (A2MR), apolipoprotein E receptor (APOER) or cluster of differentiation 91 (CD91), is a protein forming a receptor found in the plasma membrane of cells involved in receptor-mediated endocytosis. In humans, the LRP1 protein is encoded by the LRP1 gene. LRP1 is also a key signalling protein and, thus, involved in various biological processes, such as lipoprotein metabolism and cell motility, and diseases, such as neurodegenerative diseases, atherosclerosis, and cancer.

<span class="mw-page-title-main">F2RL2</span> Protein-coding gene in the species Homo sapiens

Protease activated receptor 3 (PAR-3) also known as coagulation factor II receptor-like 2 (F2RL2) and thrombin receptor-like 2, is a protein that in humans is encoded by the F2RL2 gene.

<span class="mw-page-title-main">Protease-activated receptor 2</span> Protein-coding gene in the species Homo sapiens

Protease activated receptor 2 (PAR2) also known as coagulation factor II (thrombin) receptor-like 1 (F2RL1) or G-protein coupled receptor 11 (GPR11) is a protein that in humans is encoded by the F2RL1 gene. PAR2 modulates inflammatory responses, obesity, metabolism, cancers and acts as a sensor for proteolytic enzymes generated during infection. In humans, we can find PAR2 in the stratum granulosum layer of epidermal keratinocytes. Functional PAR2 is also expressed by several immune cells such as eosinophils, neutrophils, monocytes, macrophages, dendritic cells, mast cells and T cells.

<span class="mw-page-title-main">F2RL3</span> Protein-coding gene in the species Homo sapiens

Protease-activated receptor 4 (PAR-4), also known as coagulation factor II (thrombin) receptor-like 3, is a protein that in humans is encoded by the F2RL3 gene.

Pepducins are cell-penetrating peptides that act as intracellular modulators of signal transference from receptors to G proteins. Pepducins were first developed at the Tufts Medical Center laboratories of Dr. Athan Kuliopulos and Dr. Lidija Covic.

<span class="mw-page-title-main">Cell surface receptor</span> Class of ligand activated receptors localized in surface of plama cell membrane

Cell surface receptors are receptors that are embedded in the plasma membrane of cells. They act in cell signaling by receiving extracellular molecules. They are specialized integral membrane proteins that allow communication between the cell and the extracellular space. The extracellular molecules may be hormones, neurotransmitters, cytokines, growth factors, cell adhesion molecules, or nutrients; they react with the receptor to induce changes in the metabolism and activity of a cell. In the process of signal transduction, ligand binding affects a cascading chemical change through the cell membrane.

<span class="mw-page-title-main">Aureolysin</span>

Aureolysin is an extracellular metalloprotease expressed by Staphylococcus aureus. This protease is a major contributor to the bacterium's virulence, or ability to cause disease, by cleaving host factors of the innate immune system as well as regulating S. aureus secreted toxins and cell wall proteins. To catalyze its enzymatic activities, aureolysin requires zinc and calcium which it obtains from the extracellular environment within the host.

<span class="mw-page-title-main">SCH-79797</span> Chemical compound

SCH-79797 is a drug which acts as a potent and selective antagonist of the thrombin receptor proteinase activated receptor 1 (PAR1). It has anticoagulant, anticonvulsant and antiinflammatory effects and has been researched as a treatment for heart attack and stroke, though never developed for medical use. It also shows antibiotic actions which are not shared with other PAR1 antagonists such as vorapaxar, so may be mediated through a different target than PAR1.

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Further reading

This article incorporates text from the United States National Library of Medicine, which is in the public domain.