N-linked Glycosylation of Protease-Activated Receptor

Besides their functions in protein degradation and digestion, proteases also serve as hormone-like signaling molecules that control critical pathophysiological processes in the body namely; pain and repair mechanisms, homeostasis and inflammation. Different types of proteases can communicate with the cells by splitting a protease activated receptors (PARs), which is a member of the four-G protein-coupled receptors (Zhao, Matthew and Nigel n.p). PARs manifested by nearly all types of cells regulates the critical psychological and disease-related processes and are now the most frequent target in therapy for primary prevalent diseases. To get more insight into the PARs activation and performance we can consider the relations of thrombin in PAR1, PAR3, and PAR4. And trypsin in the case of PAR2 and PAR4.These proteases reveal the tethered ligands, which helps in the stabilization of the conformed cleaving receptors
activating the canonical pathway.
PAR1 is a G-protein coupled receptor (GPCR) that plays a significant role in the
Coagulation of the protease thrombin. PAR1 intertwines well to multiple heterotrimeric G-protein subgroups when in the same cell hence promoting cellular responses. However, it is still unclear on how the molecular processes and mechanism by which an activation of a particular GPCR on the same ligand allows coupling to many G proteins subsets (Soto et al. n.p).
An experiment conducted proved that PAR1 mutant which was deficient in glycosylation at extracellular loop 2 (ECL2) was more reliable at stimulating Gq-linked phosphoinositide communications in comparison with glycosylated wild-type receptor.

In another event, wild type PAR1 was more efficient at G12/13 dependent RhoA activation concerning the mutant receptor not glycolysed at ECL2.Another experiment involving the use of endogenous PAR1 deglycolysed using tunicamycin, a glycoprotein synthetic inhibitor also showed increased PI index and diminished off RhoA activation contrary to the native inhibitor. The protease thrombin is generated any time there are vascular injury and inflammation. It promotes thrombosis, inflammation and proliferative responses and homeostasis.
PAR1 belongs to the prototypical family of four GPCRs that receive activation from particular protease, included in the list is protease thrombin (Soto et al n.p).The thrombin activates PAR1 through proteolytic spitting of the extracellular N-terminus, which uncovers a new N-terminus domain. The coagulation stream and the PARs jointly provide a brilliant mechanism that connects mechanical signals in the form of tissue injury cells related responses. These receptors to a great extent seem to explain cellular effects of thrombin. They also resolve to pass off information to other protease-like trypsin (Coughlin 1800).
Thrombin triggers many own responses in platelets, endothelial and others. PARs and GPCRs work in unison by exploiting the complicated mechanism in the conversion of the extracellular cleavage occurrence into a trans-membrane signal. G-protein coupled receptors PAR3, and PAR1 mediates signaling to thrombin. When thrombin cleaves N-terminus domain, unmasking of the new N-terminus that functions as tethered ligands binding intermolecular to the receptor’s body occur. This leads to the initiation of transmembrane signaling.

The function of protease in the PARs activation is sole to expose receptors tethered ligand. The pattern at the leading to thrombin cleavage appears to back up this finding fully. Similar to other G-protein coupled receptors, PAR1 is quickly uncoupled from sending and receiving signals soon after activation. According to the results from the findings endogenous PAR1 deficient in glycosylation showed improved G-protein mediated reactions and decreased RhoA activation, as opposed to the native receptor (Zhao, Matthew and Nigel n.p). With the findings from many previous experiments; these results regarding N-linked glycosylation takes the knowledge for this discipline a notch higher.
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Works cited
Coughlin, Shaun. “Protease-activated receptors in hemostasis, thrombosis and vascular biology.” Journal of Thrombosis and Haemostasis 3.8 (2005): 1800-1814. Web
Soto, Antonio, et al. “N-linked glycosylation of protease-activated receptor-1 at extracellular loop 2 regulates G-protein signaling bias.” Proceedings of the National Academy of Sciences 112.27 (2015): E3600-E3608. Print
Zhao, Peishen, Matthew Metcalf, and Nigel Bunnett. “Biased signaling of protease-activated receptors.” Frontiers in endocrinology 5.76 (2014): 1-16. Print