Structure Rearrangement And Monomeric Isomer’s Function Of C-reactive Protein

C-reactive protein (CRP) has long been used in clinical examination as an inflammation marker for acute inflammatory responses. Recent evidences indicate that CRP also plays a role in development of cardiovascular diseases (CVD) that are associated with inflammation. In addition to be a sensitive predictor, CRP may directly participate in the inflammatory processes of atherosclerosis and thrombosis. However, the underlying mechanisms by which CRP functions in the pathopHysiologic process remain elusive and the results are conflicting concerning the role of CRP in the blood vessel wall. Some of the apparently contradictory actions of CRP may be attributed to different methods applied, but are more likely to be due to the existence of two distinct conformations of CRP, the pentameric (pCRP) and monomeric CRP (mCRP) forms.We propose here that pCRP, which consists of five identical subunits, is a form of "protein storage", and monomeric CRP (mCRP), which is probably generated by dissociation of pCRP in inflammatory loci, is the functional form. However, little is known about the molecular mechanisms that controls the generation and functions of mCRP. Herein, we found that pCRP could bind to and be internalized by monocyte, probably through cell receptor. Through sodium dodecyl sulfate polyacrylamide gele electropHoresis (1/20), fluorescence analysis and enzyme-linked immuno sorbent assay, it was found that pCRP could rapidly convert to mCRP with the presence of reactive oxygen species under mild acidic pH condition, which conditions is common at inflammatory lesions. We further identified Cu2+-H2O2 system as a specific inducer that could trigger the dissociation of pCRP through the binding of Cu2+ and pCRP. The release of Cu2+ from ceruloplasmin during oxidative stress could provide the required ion for the dissociation. In summary, we propose a rearrangement model of pCRP. The surgent pCRP in acute pHase could bind to and be internalized by monocyte, followed by migration of monocytes carrying pCRP from the blood to the inflammatory loci. Mild acidic pH and reactive oxygen species in inflammatory lesions could further induce the production of mCRP. This explains how the acute change of pCRP anount, which a dynamic range of> 1,000-fold within hours could function in a fine manner in sopHisticated cellular responses and pathological processes at local lesion.Furthermore, we identified that mCRP is the major isoform that binds fibronectin (FN), regardless of solid or liquid pHase. This is an indirect proof that mCRP, rather than pCRP, is involved in wound healing in the early stages of CVD. Peptide competition analysis indicated that the bingding of mCRP and FN is mediated by the putative cholesterol binding consensus sequence of CRP (aa 35-47). The binding could promote monocyte adhesion to immobilized FN, which indicated pro-inflammatory activities of mCRP in early lesions. In addition, animal experiments with mice and rabbits confirmed that mCRP (especially reduced mCRP) has potent biological effect on the expression of interleukin. In conclusion, expression of pro-inflammatory properties of CRP requires sequential conformational changes, i.e. loss of pentameric symmetry followed by reduction of the intra-subunit disulfide bond which is the "function switch" in CRP function.