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= Human C-reactive protein (CRP) = | = Human C-reactive protein (CRP) =<ref>PMID:10368284</ref> <ref>PMID:15337754</ref> | ||
The C-reactive protein (CRP) is a plasma protein, mainly synthesized by the liver. Its concentration may increase rapidly, as much as 1000-fold or more, in response to tissue injury, infection and inflammation: It's an acute-phase protein. | The C-reactive protein (CRP) is a plasma protein, mainly synthesized by the liver. Its concentration may increase rapidly, as much as 1000-fold or more, in response to tissue injury, infection and inflammation: It's an acute-phase protein. | ||
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== '''Structure of CRP''' == | == '''Structure of CRP''' ==<ref>PMID:10368284</ref> | ||
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Each protomer has a recognition face (also called face B) with a phosphocholine binding site (carrying two calcium ions), made of a two-layered β sheet. The other face - the effector face (or face A) - where complement C1q and Fc receptors bind, contains a single α helix. Consequently, the pentamer consists of five α helices on one side, and ten calcium ions on the other. | Each protomer has a recognition face (also called face B) with a phosphocholine binding site (carrying two calcium ions), made of a two-layered β sheet. The other face - the effector face (or face A) - where complement C1q and Fc receptors bind, contains a single α helix. Consequently, the pentamer consists of five α helices on one side, and ten calcium ions on the other. | ||
== '''The Calcium and Phosphocholine binding sites''' == | == '''The Calcium and Phosphocholine binding sites''' ===<ref>PMID:10368284</ref> | ||
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==='''''Calcium'''''=== | ==='''''Calcium'''''====<ref>PMID:10368284</ref> | ||
There are two <scene name='56/568019/Structure_of_crp_v2/1'>calcium-binding sites</scene> per CRP protomer. | There are two <scene name='56/568019/Structure_of_crp_v2/1'>calcium-binding sites</scene> per CRP protomer. | ||
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==='''''Phosphocholine'''''=== | ==='''''Phosphocholine'''''====<ref>PMID:10368284</ref> | ||
Phosphocholine is an universal phospholipid found particularly in the cell membranes and plasma lipoproteins of bacteria, fungi, plants and other eukaryotic organisms whose us, the human beings. However, CRP can only bind phosphocholine of our damaged or apoptotic cells, as head groups of phosphocholine are inaccessible to CRP in “normal” cells. | Phosphocholine is an universal phospholipid found particularly in the cell membranes and plasma lipoproteins of bacteria, fungi, plants and other eukaryotic organisms whose us, the human beings. However, CRP can only bind phosphocholine of our damaged or apoptotic cells, as head groups of phosphocholine are inaccessible to CRP in “normal” cells. | ||
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== '''Interaction with C1q and Fcγ receptors''' == | == '''Interaction with C1q and Fcγ receptors''' == | ||
[[Image:C1q.3.jpg]] | [[Image:C1q.3.jpg]]<ref>PMID:10368284</ref> | ||
C1 is the first component of the classical pathway of the complement and consists of a complex of one C1q, two C1r, and two C1s molecules. C1q is the recognition subunit whereas C1r and C1s form the catalytic subunit. C1q is composed of three different polypeptide chains A, B and C and has a total molecular mass of 460Da. Each chain is present in four copies in the C1q molecule. C1q can bind different activator such as immunoglobulin (IgM and IgG) and CRP. In red, adjacent bound CRP molecules may present multiple binding sites via the A face for the C1q arms. | C1 is the first component of the classical pathway of the complement and consists of a complex of one C1q, two C1r, and two C1s molecules. C1q is the recognition subunit whereas C1r and C1s form the catalytic subunit. C1q is composed of three different polypeptide chains A, B and C and has a total molecular mass of 460Da. Each chain is present in four copies in the C1q molecule. C1q can bind different activator such as immunoglobulin (IgM and IgG) and CRP. In red, adjacent bound CRP molecules may present multiple binding sites via the A face for the C1q arms. | ||
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Various studies have shown that CRP is able to bind to Fcγ receptor with an affinity comparable to that of IgG. These receptors expressed on hematopoietic cells are able to recognize the Fc portion of IgG. They induce phagocytosis in response to immune system attack. The interaction of CRP with Fcγ receptor suggests that CRP has an important role in the immune system and could explain that CRP concentration increases during the acute phase of the inflammation. | Various studies have shown that CRP is able to bind to Fcγ receptor with an affinity comparable to that of IgG. These receptors expressed on hematopoietic cells are able to recognize the Fc portion of IgG. They induce phagocytosis in response to immune system attack. The interaction of CRP with Fcγ receptor suggests that CRP has an important role in the immune system and could explain that CRP concentration increases during the acute phase of the inflammation. | ||
==References== | |||
<references />. | |||
