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Protein S
 
 
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Protein S is a vitamin K
Vitamin K

Vitamin K denotes a group of lipophilic, hydrophobic vitamins that are needed for the posttranslational modification of certain proteins, mostly required for blood coagulation....
-dependent plasma glycoprotein
Glycoprotein

Not to be confused with peptidoglycan or proteoglycan.Glycoproteins are proteins that contain oligosaccharide chains covalently attached to their Peptide side-chains....
 synthesized in the liver. In the circulation, Protein S exists in two forms: a free form and a complex form bound to complement
Complement system

The complement system is a biochemical cascade that helps clear pathogens from an organism. It is part of the larger immune system that is not adaptable and does not change over the course of an individual's lifetime; as such it belongs to the innate immunity....
 protein C4b.

best characterized function of Protein S is its role in the anti coagulation
Coagulation

Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis , wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop hemorrhage and begin repair of the damaged vessel....
 pathway, it functions as a cofactor to Protein C
Protein C

Protein C is a major physiological anticoagulant. It is a vitamin K-dependent serine protease enzyme that is activated by thrombin into activated protein C ....
 in the inactivation of Factors Va
Factor V

Factor V is a protein of the coagulation system, rarely referred to as proaccelerin or labile factor. In contrast to most other coagulation factors, it is not enzymatically active but functions as a cofactor....
 and VIIIa
Factor VIII

Factor VIII is an essential thrombusting factor. In humans, Factor VIII is encoded by the F8 gene. Defects in this gene results in hemophilia A, a common Dominance_#Recessive_trait X-linked coagulation disorder....
. Only the free form has cofactor activity.

Protein S can bind to negatively charged phospholipids via the carboxylated GLA domain.






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Encyclopedia


Protein S is a vitamin K
Vitamin K

Vitamin K denotes a group of lipophilic, hydrophobic vitamins that are needed for the posttranslational modification of certain proteins, mostly required for blood coagulation....
-dependent plasma glycoprotein
Glycoprotein

Not to be confused with peptidoglycan or proteoglycan.Glycoproteins are proteins that contain oligosaccharide chains covalently attached to their Peptide side-chains....
 synthesized in the liver. In the circulation, Protein S exists in two forms: a free form and a complex form bound to complement
Complement system

The complement system is a biochemical cascade that helps clear pathogens from an organism. It is part of the larger immune system that is not adaptable and does not change over the course of an individual's lifetime; as such it belongs to the innate immunity....
 protein C4b.

Function

The best characterized function of Protein S is its role in the anti coagulation
Coagulation

Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis , wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop hemorrhage and begin repair of the damaged vessel....
 pathway, it functions as a cofactor to Protein C
Protein C

Protein C is a major physiological anticoagulant. It is a vitamin K-dependent serine protease enzyme that is activated by thrombin into activated protein C ....
 in the inactivation of Factors Va
Factor V

Factor V is a protein of the coagulation system, rarely referred to as proaccelerin or labile factor. In contrast to most other coagulation factors, it is not enzymatically active but functions as a cofactor....
 and VIIIa
Factor VIII

Factor VIII is an essential thrombusting factor. In humans, Factor VIII is encoded by the F8 gene. Defects in this gene results in hemophilia A, a common Dominance_#Recessive_trait X-linked coagulation disorder....
. Only the free form has cofactor activity.

Protein S can bind to negatively charged phospholipids via the carboxylated GLA domain. This property allows Protein S to function in the removal of cells which are undergoing apoptosis
Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
. Apoptosis
Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
 is a form of cell death that is used by the body to remove unwanted or damaged cells from tissues. Cells which are apoptotic (ie. in the process of apoptosis
Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
) no longer actively manage the distribution of phospholipids in their outer membrane and hence begin to display negatively charged phospholipids, such as phosphatidyl serine, on the cell surface. In healthy cells, an ATP (Adenosine triphosphate
Adenosine triphosphate

This article is about the chemical used by cells as an energy carrier. For other uses, see ATP .Adenosine-5'-triphosphate is a multifunctional nucleotide, and plays an important role in cell biology as a coenzyme that is the "molecule unit of currency" of intracellular energy transfer....
)-dependent enzyme removes these from the outer leaflet of the cell membrane. These negatively charged phospholipids are recognized by phagocytes such as macrophages. Protein S can bind to the negatively charged phospholipids and function as a bridging molecule between the apoptotic cell and the phagocyte. The bridging property of Protein S enhances the phagocytosis of the apoptotic cell, allowing it to be removed 'cleanly' without any symptoms of tissue damage such as inflammation
Inflammation

Inflammation is the complex biological response of Blood vessel tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. It is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue....
 occurring.

Pathology


Protein S deficiency
Protein S deficiency

Protein S deficiency is a disorder associated with increased risk of venous thrombosis. Protein S, a vitamin K-dependent physiological anticoagulant, acts as a nonenzymatic cofactor to activated protein C in the proteolytic degradation of factor Va and factor VIIIa....
 is a rare blood disorder which can lead to an increased risk of thrombosis
Thrombosis

Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot, because the first step in repairing it is to prevent loss of blood....
.

See also

  • hemostasis
    Hemostasis

    Hemostasis is a complex process which causes the bleeding process to stop. Most time this includes the changing of blood from a fluid to a solid state....


Further reading