Calcium (Ca+2) Binding
Figure 4: Calcium Binding sites of human pentraxins in comparison to hCRP(Source; Original)
As previously mentioned, hCRP has calcium dependant binding interactions, where 2 calcium ions are bonded
to hCRP through hydrophobic amino acid sites. Figure 4 illustrates the amino acid sites that the calcium
binding occurs through in comparison to other human pentraxins. First calcium binding occurs through the
amino acids; Asp 60, Asn 61, Glu 138, Asp 140, Gln 139, while the second calcium binding occurs through the
amino acids; Glu 138, Asp 140, Gln 150 and Glu 147 (Shrive et al., 1996). Human SAP has the most amino
acid similarity with hCRP calcium binding sites, while hPTX3 and hPTX4 shows no similarity with hCRP calcium
binding sites. PTX3 is known to not have any binding interactions with Pc, which suggests an association with
the lack of calcium binding sites.
Figure 5: Molecular structures of amino acids that calcium binding interactions occur through in hCRP (Source:
Original)
As shown in figure 5, calcium binding occurs through four different amino acids exclusively where all of the
amino acids contains carboxyl groups which upon deprotonation becomes negatively charged. Since calcium
is a positively charged ion, binding interaction with these amino acids can occur. Furthermore, Ho et al. (2007)
suggests that the amino acids of interest has some of the strongest binding strengths. On the other hand, as
shown in figure 6, the hCRP-Ca interaction occurs through a more hydrophobic site compared to other binding
interactions. The green sites in figure 6 represents hydrophobic sites while red sites represents hydrophilicity.
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