Sandbox Reserved 1121: Difference between revisions

Thereafter, the ligand-binding face of the molecule will be called B and the opposite face will be called A. The B face binds two Ca²⁺ ions and a phosphocholine per subunit. The A face, recognizable by the presence of an α-helix and a deep cavity, can interact with C1q and Fc receptors <ref name="duclos">PMID: 15531769 </ref>.   

CRP is a calcium dependent structure. In fact, Ca²⁺ is required for PC binding, and more precisely for the formation of the PC-binding site thanks to structural rearrangements. The protection against denaturation and proteolysis is also performed through Ca²⁺-binding. In the absence of Ca²⁺, hCRP is cleaved between Asn145 and Phe146 by nagarse protease, and between Phe146 and Glu147 by pronase.  

Asp60, Asn61, Glu138, Asp140 and the main-chain carbonyl of Gln139 residues allow the first calcium ion binding, and the second is performed through Glu138, Asp140, Glu147 and Gln150 <ref name="ramadan">PMID: 12037301</ref>.

The two Ca²⁺-binding sites are overlapping in a loop. In the absence of Ca²⁺, the loop changes conformation and releases the proteolysis site. Therefore Ca²⁺ protects CRP form proteolytic cleavage <ref name="agrawal"/>.

PC stands for phosphocholine. It is a phospholipid in cell membranes and a plasma lipoprotein <ref name="thompson"/>. The PC-binding site is a hydrophobic pocket constituted by the residues Leu64, Phe66, Thr76 and the two Ca²⁺ <ref name="agrawal"/>.

The choline function of PC interacts with the two key residues Phe66 and Glu81, therefore PC lies inside the PC-binding site <ref name="kumar"/> <ref name="agrawal"/>.