Structure
Figure 3: Three dimensional structure of hCRP-Pc complex, (a) effector face of hCRP, (b) recognition face of hCRP.
Source: Adapted from (Thompson, Pepys and Wood, 1999)
Structurally, hCRP is made up of 5 sub-units arranged around a central pore to make up a pentameric radial
(Shrive et al., 1996). Each sub-unit, which are called protomers, consists of 206 amino acids and forms a cyclic
pentamer. Protomers that are linked to each other by non-covalent bonds, have the symmetry of flattened
jelly roll appearance (Shrive et al., 1996; Volanakis, 2001; Agrawal et al., 2001). CRP has two faces where
different binding interactions occur (Shrive et al., 1996). Figure 3.a illustrates the effector face, while figure 3.b
illustrates the recognition face where the calcium and phosphocholine binding interactions occur (Thompson
et al., 1999). In terms of quaternary protein structure, hCRP is made up of two antiparallel β-sheets and an
α-helix (Shrive et al., 1996). As shown in figue 3.a, α-helix is found on the effector face of the hCRP, folded on
top of one of the β-sheets (Szalai et al., 1997).
CRP has calcium dependent binding interactions, where each protomer binds to two calcium ions in order for
other binding interactions to occur. As shown in figure 3.b, binding interactions with 2 calcium ions (Ca+2)
occur on the recognition face of the protein (Thompson et al., 1999). Ramadan et al. (2002) suggests that
calcium binding causes slight conformational changes which makes CRP-Pc complex more stable.
Bioinformatic Investigation of Binding Interactions
CRP is known to have binding interactions with many receptors and ligands. However, in this study the most
important three interaction was investigated as a part of the final year undergraduate independent research
project, where bioinformatics investigation of key structures of hCRP was an important part of the study in
gaining a better understanding of the protein.
HCRP works by activating the complement system of the innate immune system via C1q of the classical
pathway (Szalai et al., 1997). However in order to activate the complement system, hCRP needs to be bonded
to a physiological ligand which is usually the Phosphocholine (Pc) that is found within the C-polysaccharide
(CWPS) molecule (Szalai et al., 1997). On the other hand, hCRP is calcium dependent, which means that in
order to have other binding interactions, it has to make bonds with two calcium ions, where as previously
indicated, it is thought to make the CRP complexes more stable (Volanakis and Kaplan, 1971; Ramadan et al.,
2002).
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