**2. Overall structure**

CRP is a protein of the pentraxins group, which is distinguished by its conformation in the space, presenting pentameric form of annular disc (see **Figure 1**). Structurally, it is composed of five identical subunits unglycosylated and linked by noncovalent bonds that depend of calcium binding to exert their action [16]. From a functional perspective, the active forms of PCR are the pentameric or native structure (p-n-PCR or PCR) and the monomeric isoform (m-PCR). This latter is formed by a dissociation process of the p-PCR. The monomeric isoform may appear linked to membranes or free in plasma, changing their functions in each case [17]. The pentameric isoform has two faces, one with ability to adhere to the phosphatidylcholine in the presence of calcium ions [18], while the other presents adhesion sites for complement component C1q and Fc receptors. The existence of five subunits with capacity to bind together phosphatidylcholine determines its high avidity for phosphatidylcholine [18]. This interaction occurs during the identification of microorganisms such as bacteria, fungi, and parasites showing phosphatidylcholine in their membrane [19]. Once identified pathogens, adherence to C1q occurs on the other side of the pentamer, activating partially the complement pathway and adhering to factor H [17]. This mechanism is a first defensive barrier in our organism against certain pathogens.

Obesity and Its Influence on Mediators of Inflammation: Clinical Relevance of C-Reactive Protein in Obese Subjects http://dx.doi.org/10.5772/64881 75

**Figure 1.** Crystal structure of C-reactive protein complexed with phosphocholine from Thompson et al. [50].
