Lauren Ferris/Sandbox 1
From Proteopedia
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| - | + | =Activated Protein C= | |
<Structure load='1aut' size='400' color='white' frame='true' align='left' caption='pdb: 1AUT' /> | <Structure load='1aut' size='400' color='white' frame='true' align='left' caption='pdb: 1AUT' /> | ||
| - | + | ==Introduction== | |
The vitamin K dependent zymogen Protein C is an integral component of the blood coagulation system. The blood coagulation system is composed of two pathways that converge to form the prothrombinase complex (FVa-FXa). Thrombin is generated from this complex and catalyzes the formation of the clot by activating Fibrinogen and FXIII. Thrombin will also bind to thrombomodulin and the complex removes 12 peptides(Arg169-Leu170) from the protein, converting the protein to the active form: Activated Protein C.<ref name="thrombo">PMID: 3029867</ref><ref name="thromboII">PMID: 8236111 </ref><ref name="thromboIII">PMID: 1912552 </ref> Activated Protein C will function as a down-regulator of procoagulant stimuli through the degradation of zymogens and their active counterparts: FV/FVa and FVIII/FVIIIa. <ref name="difI">PMID: 6687387 </ref><ref name="difII">PMID: 1939075</ref> This ability enables Protein C to modulate the coagulant response, preventing unchecked clotting. | The vitamin K dependent zymogen Protein C is an integral component of the blood coagulation system. The blood coagulation system is composed of two pathways that converge to form the prothrombinase complex (FVa-FXa). Thrombin is generated from this complex and catalyzes the formation of the clot by activating Fibrinogen and FXIII. Thrombin will also bind to thrombomodulin and the complex removes 12 peptides(Arg169-Leu170) from the protein, converting the protein to the active form: Activated Protein C.<ref name="thrombo">PMID: 3029867</ref><ref name="thromboII">PMID: 8236111 </ref><ref name="thromboIII">PMID: 1912552 </ref> Activated Protein C will function as a down-regulator of procoagulant stimuli through the degradation of zymogens and their active counterparts: FV/FVa and FVIII/FVIIIa. <ref name="difI">PMID: 6687387 </ref><ref name="difII">PMID: 1939075</ref> This ability enables Protein C to modulate the coagulant response, preventing unchecked clotting. | ||
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| - | + | ==Structure== | |
Activated protein C is a spheroid shaped molecule with both alpha helices and beta sheets. The protein contains similar domains to other vitamin K dependent coagulation proteins with a heavy and light chain connected by a di-sulfide bond. The light chain contains a Gla domain and 2 epidermal growth factor domains, while the heavy chain contains an activated peptide domain and a serine protease domain. | Activated protein C is a spheroid shaped molecule with both alpha helices and beta sheets. The protein contains similar domains to other vitamin K dependent coagulation proteins with a heavy and light chain connected by a di-sulfide bond. The light chain contains a Gla domain and 2 epidermal growth factor domains, while the heavy chain contains an activated peptide domain and a serine protease domain. | ||
The Gla domain contains glutamic acids which are converted to y-carboxyglutamic acid by a Vitamin K dependent reaction. The y-carboxyglutamic acid enables the protein to bind to Ca2+ and undergo a conformational change that enables binding to a phospholipid bilayer. | The Gla domain contains glutamic acids which are converted to y-carboxyglutamic acid by a Vitamin K dependent reaction. The y-carboxyglutamic acid enables the protein to bind to Ca2+ and undergo a conformational change that enables binding to a phospholipid bilayer. | ||
| - | The Epidermal Growth Factor Domains are referenced as EGF-1 and EGF-2, with EGF-1 being proximal to the c-terminal domain and EGF-2 being proximal to the n-terminal domain. Protein C has a heavy and light chain and a cleavage after EGF2 results in the formation of two polypeptides, with Gla, EGF1, and EGF2, forming the light chain. <scene name='Lauren_Ferris/Sandbox_1/Egf2/1'>EGF2</scene> | ||
| - | + | ====Epidermal Growth Factor==== Domain 1. EGF-1. This domain is proximal to the n-terminal domain. Activated Protein C EGF-1 contains a unique seven residue insert and an extra-disulfide compared to other EGF domains in other proteins. This gives the protein a total of four di-sulfide bridges existing between Cys50-69, Cys59-64,and Cys63-78 and 80-89. Three major loops are formed from these disulfides. The first loop is actually composed of two loops with Cys 50-69 forming a larger loop and Cys 59-64 forming a smaller loop inside. The terminal residues of EGF1 83-85 form an anti-parallel pleated sheet with residues 91-93 to connect to EGF2. | |
| - | + | ====Epidermal Growth Factor Domain 2==== EGF-2. This domain is sometimes referenced as the c-terminal EGF-2, although it is adjacent to EGF1. EGF-2 is a fairly standard EGF domain containing disulfide bridges that form loops. Activated protein C contains both a heavy and light chain. The light chain includes residues from the N-terminus of the protein to several residues after the C terminus of the EGF-2 domain. | |
| + | |||
| + | ====Serine Protease Domain==== The serine protease domain is made up of two six stranded antiparallel beta barrel domains that cross through the core. The barrel domains also form loops that help to comprise the surface of this domain. The protein contains structural elements such as a buried ion pair, an active site between barrel domains, surface helices, di-sulfides, and a Ca2+ binding loop. Unique to Protein C include n-terminal leucine next to the active site. | ||
| + | |||
| + | =====Surface Structure===== A cluster of positive charges have been observed. Based on homology, this region is thought to be involved with substrate and inhibitor interactions with the protein. An insertion lending to a helix forming, and a loop at the edge of the catalytic site also exist. | ||
| + | |||
| + | =====Active Site Structure===== Active site contains Histidine 211, Aspartic Acid 257, and Serine 360. The only structural hinderance preventing binding to the active site is a 60 residue loop. Other loops also help to form a deep depression near the active site. | ||
---- | ---- | ||
| - | + | ==Mechanism== | |
Activated Protein C is a serine protease and utilizes residues Aspartic Acid 257, Histidine 211, and Serine 360 to cleave factors FV and FVIII as well as their activated forms. Protein C has been shown to be a highly functional enzyme functioning in the presence of membrane bound and unbound substrate, while being resistant to a variety of inhibitors. Activate Protein C has been shown to cleave FV only in the presence of a phospholipid bilayer at Arg 306 first, followed by Arg 506, and then Arg 679 and Lys 994. Under these conditions cleavage at Arg 306 is insufficient for inactivation. Activated Protein C can also degrade FVa....... | Activated Protein C is a serine protease and utilizes residues Aspartic Acid 257, Histidine 211, and Serine 360 to cleave factors FV and FVIII as well as their activated forms. Protein C has been shown to be a highly functional enzyme functioning in the presence of membrane bound and unbound substrate, while being resistant to a variety of inhibitors. Activate Protein C has been shown to cleave FV only in the presence of a phospholipid bilayer at Arg 306 first, followed by Arg 506, and then Arg 679 and Lys 994. Under these conditions cleavage at Arg 306 is insufficient for inactivation. Activated Protein C can also degrade FVa....... | ||
Protein C functions best in the presence of a phospholipid bilayer and with its cofactor Protein S. | Protein C functions best in the presence of a phospholipid bilayer and with its cofactor Protein S. | ||
---- | ---- | ||
| - | + | ==Related Proteins== | |
In general, protein C has a high degree of homology to other vitamin k dependent serine proteases. These Gla domain containing proteins include but are not limited to blood coagulation proteins. Non-blood coagulation proteins include trypsin and chymotrypsin. Coagulation proteins with a high degree of homology include prothrombin, Factor VII, Factor IX, and Factor X. Protein S and Protein Z are also fairly homologous, but they are not serine proteases. Despite the similarity in structure, the enzymes retain a high degree of specificity for their substrates, perhaps due to the nonhomologous surface loops that are away from the substrate binding pocket. | In general, protein C has a high degree of homology to other vitamin k dependent serine proteases. These Gla domain containing proteins include but are not limited to blood coagulation proteins. Non-blood coagulation proteins include trypsin and chymotrypsin. Coagulation proteins with a high degree of homology include prothrombin, Factor VII, Factor IX, and Factor X. Protein S and Protein Z are also fairly homologous, but they are not serine proteases. Despite the similarity in structure, the enzymes retain a high degree of specificity for their substrates, perhaps due to the nonhomologous surface loops that are away from the substrate binding pocket. | ||
---- | ---- | ||
| - | + | ==Links to Available Structures== | |
The Protein Data Bank has Human Acitvated Protein C - [http://www.rcsb.org/pdb/explore/explore.do?structureId=1AUT 1AUT] | The Protein Data Bank has Human Acitvated Protein C - [http://www.rcsb.org/pdb/explore/explore.do?structureId=1AUT 1AUT] | ||
The Protein Data Bank has Human Activated Protein C complexed with PPACK - [http://www.rcsb.org/pdb/explore/explore.do?structureId=3F6U 3F6U] | The Protein Data Bank has Human Activated Protein C complexed with PPACK - [http://www.rcsb.org/pdb/explore/explore.do?structureId=3F6U 3F6U] | ||
---- | ---- | ||
| - | + | ==Interesting Facts== | |
Copperhead snake venom is thought to contain protein c activators. | Copperhead snake venom is thought to contain protein c activators. | ||
---- | ---- | ||
| - | + | ==References and Notes== | |
<references/> | <references/> | ||
Revision as of 05:07, 15 May 2012
Contents |
Activated Protein C
|
Introduction
The vitamin K dependent zymogen Protein C is an integral component of the blood coagulation system. The blood coagulation system is composed of two pathways that converge to form the prothrombinase complex (FVa-FXa). Thrombin is generated from this complex and catalyzes the formation of the clot by activating Fibrinogen and FXIII. Thrombin will also bind to thrombomodulin and the complex removes 12 peptides(Arg169-Leu170) from the protein, converting the protein to the active form: Activated Protein C.[1][2][3] Activated Protein C will function as a down-regulator of procoagulant stimuli through the degradation of zymogens and their active counterparts: FV/FVa and FVIII/FVIIIa. [4][5] This ability enables Protein C to modulate the coagulant response, preventing unchecked clotting.
Protein C has also been recognized for its role in anti-inflammatory and cytoprotective signaling responses in endothelial cells. Protein C will bind to an endothelial protein c receptor (EPCR) and then activate protease-activated receptor (PAR-1).[6]
Protein C is synthesized in the liver and circulates the blood at a concentration of 4 ug/mL. The liver conformation is a single polypeptide sequence with an additional 42 amino acids attached at the N-terminus. This structure is known as the pre-pro sequence. Subsequent removal of these peptides as well as Lys156-Arg157 will result in the 62 kD protein that is often observed.[7]
Structure
Activated protein C is a spheroid shaped molecule with both alpha helices and beta sheets. The protein contains similar domains to other vitamin K dependent coagulation proteins with a heavy and light chain connected by a di-sulfide bond. The light chain contains a Gla domain and 2 epidermal growth factor domains, while the heavy chain contains an activated peptide domain and a serine protease domain.
The Gla domain contains glutamic acids which are converted to y-carboxyglutamic acid by a Vitamin K dependent reaction. The y-carboxyglutamic acid enables the protein to bind to Ca2+ and undergo a conformational change that enables binding to a phospholipid bilayer.
====Epidermal Growth Factor==== Domain 1. EGF-1. This domain is proximal to the n-terminal domain. Activated Protein C EGF-1 contains a unique seven residue insert and an extra-disulfide compared to other EGF domains in other proteins. This gives the protein a total of four di-sulfide bridges existing between Cys50-69, Cys59-64,and Cys63-78 and 80-89. Three major loops are formed from these disulfides. The first loop is actually composed of two loops with Cys 50-69 forming a larger loop and Cys 59-64 forming a smaller loop inside. The terminal residues of EGF1 83-85 form an anti-parallel pleated sheet with residues 91-93 to connect to EGF2.
====Epidermal Growth Factor Domain 2==== EGF-2. This domain is sometimes referenced as the c-terminal EGF-2, although it is adjacent to EGF1. EGF-2 is a fairly standard EGF domain containing disulfide bridges that form loops. Activated protein C contains both a heavy and light chain. The light chain includes residues from the N-terminus of the protein to several residues after the C terminus of the EGF-2 domain.
====Serine Protease Domain==== The serine protease domain is made up of two six stranded antiparallel beta barrel domains that cross through the core. The barrel domains also form loops that help to comprise the surface of this domain. The protein contains structural elements such as a buried ion pair, an active site between barrel domains, surface helices, di-sulfides, and a Ca2+ binding loop. Unique to Protein C include n-terminal leucine next to the active site.
=====Surface Structure===== A cluster of positive charges have been observed. Based on homology, this region is thought to be involved with substrate and inhibitor interactions with the protein. An insertion lending to a helix forming, and a loop at the edge of the catalytic site also exist.
=====Active Site Structure===== Active site contains Histidine 211, Aspartic Acid 257, and Serine 360. The only structural hinderance preventing binding to the active site is a 60 residue loop. Other loops also help to form a deep depression near the active site.
Mechanism
Activated Protein C is a serine protease and utilizes residues Aspartic Acid 257, Histidine 211, and Serine 360 to cleave factors FV and FVIII as well as their activated forms. Protein C has been shown to be a highly functional enzyme functioning in the presence of membrane bound and unbound substrate, while being resistant to a variety of inhibitors. Activate Protein C has been shown to cleave FV only in the presence of a phospholipid bilayer at Arg 306 first, followed by Arg 506, and then Arg 679 and Lys 994. Under these conditions cleavage at Arg 306 is insufficient for inactivation. Activated Protein C can also degrade FVa....... Protein C functions best in the presence of a phospholipid bilayer and with its cofactor Protein S.
Related Proteins
In general, protein C has a high degree of homology to other vitamin k dependent serine proteases. These Gla domain containing proteins include but are not limited to blood coagulation proteins. Non-blood coagulation proteins include trypsin and chymotrypsin. Coagulation proteins with a high degree of homology include prothrombin, Factor VII, Factor IX, and Factor X. Protein S and Protein Z are also fairly homologous, but they are not serine proteases. Despite the similarity in structure, the enzymes retain a high degree of specificity for their substrates, perhaps due to the nonhomologous surface loops that are away from the substrate binding pocket.
Links to Available Structures
The Protein Data Bank has Human Acitvated Protein C - 1AUT
The Protein Data Bank has Human Activated Protein C complexed with PPACK - 3F6U
Interesting Facts
Copperhead snake venom is thought to contain protein c activators.
References and Notes
- ↑ Esmon CT. The regulation of natural anticoagulant pathways. Science. 1987 Mar 13;235(4794):1348-52. PMID:3029867
- ↑ Esmon CT. Molecular events that control the protein C anticoagulant pathway. Thromb Haemost. 1993 Jul 1;70(1):29-35. PMID:8236111
- ↑ Stenflo J. Structure-function relationships of epidermal growth factor modules in vitamin K-dependent clotting factors. Blood. 1991 Oct 1;78(7):1637-51. PMID:1912552
- ↑ Suzuki K, Stenflo J, Dahlback B, Teodorsson B. Inactivation of human coagulation factor V by activated protein C. J Biol Chem. 1983 Feb 10;258(3):1914-20. PMID:6687387
- ↑ Fay PJ, Smudzin TM, Walker FJ. Activated protein C-catalyzed inactivation of human factor VIII and factor VIIIa. Identification of cleavage sites and correlation of proteolysis with cofactor activity. J Biol Chem. 1991 Oct 25;266(30):20139-45. PMID:1939075
- ↑ Rezaie AR. Regulation of the protein C anticoagulant and antiinflammatory pathways. Curr Med Chem. 2010;17(19):2059-69. PMID:20423310
- ↑ Brummel-Ziedin K, Orfeo T, Jenny NS, Everse SJ, and Mann KG. Wintrobe's Clinical Hematology. (2004, 11th ed) Chapter 21. Lippincott Williams and Wilkins ISBN:0781736501
