Figure 6: Three dimensional structure of hCRP-Pc, showing the CRP-Ca-Pc interaction, adapted from (Thompson,
Pepys and Wood, 1999)
Binding to Phosphocholine (Pc) of C-polysaccharide (CWPS)
CRP is known to bind to CWPS through Phosphocholine (Pc) which is a repeating tetrasaccharide unit of
CWPS. Thompson et al., (1999) proved that CRP binds to Pc through the bound calcium molecules, where
it was suggested that one of the oxygen atoms of Pc group sticks out while the other two interacts with the
calcium of hCRP. However, due to the gap in literature, the exact binding interaction and binding mechanism is
unknown since the three-dimensional structure of hCRP-CWPS complex is unknown.
Figure 7: Proposed binding mechanism of Ca-Pc complex (Source; Original)
Figure 7 was drawn, by using the findings of Thompson et al. (1999), as a hypothetical mechanism, illustrating
the binding interaction between Pc of CWPS and calcium molecules that are bound to hCRP. As shown in
figure 7, the binding interaction is thought to go through lone pair electron delocalisation which causes double
bonds to break that leads to the second oxygen of phosphate to attack to calcium ion, resulting in the first
calcium binding. On the other hand, second calcium bond is formed by the delocalisation of oxygen-phosphate
double bond, which causes the first oxygen of the phosphate to be negatively charged and attack to the second
calcium of hCRP in order to form the hCRP-Pc complex.
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