Effects of calcium, magnesium, and phosphorylcholine on secondary structures of human C-reactive protein and serum amyloid P component observed by infrared spectroscopy.
The secondary structures of human C-reactive protein (CRP) and serum amyloid P component (SAP) in D2O-based solutions in the presence or absence of calcium, magnesium, and phosphorylcholine have been investigated using Fourier transform infrared spectroscopy. Quantitative analysis provided estimations of about 50% beta-sheet, 12% alpha-helix, 24% beta-turn, and 14% unordered structure for CRP and about 54% beta-sheet, 12% alpha-helix, 25% beta-turn, and 9% unordered structure for SAP. With both proteins significant calcium-dependent changes were observed in conformation-sensitive amide I regions assigned to each type of structure. The CRP spectrum was also affected by magnesium, but the changes differed from those induced by calcium. The SAP spectrum was not affected by magnesium. Phosphorylcholine in the presence of calcium also affected the spectrum of CRP but not the spectrum of SAP. Our present study provides the first direct comparison of the secondary structures of the pentraxins human CRP and SAP and hamster female protein (Dong, A., Caughey, B., Caughey, W. S., Bhat, K. S., and Coe, J. E. (1992) Biochemistry 32, 9364-9370). These findings suggest that the three pentraxins have similar secondary structure compositions and calcium-dependent conformational changes, but differ significantly in their responses to phosphorylcholine and magnesium. Such properties are expected to be relevant to the incompletely understood roles of these highly conserved proteins including binding to nuclear proteins, complement activation, and association with amyloids.
Dong
A
A
Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins 80523.
Caughey
W S
WS
Du Clos
T W
TW
D002097:C-Reactive Protein / Q000737:chemistry* / Q000187:drug effects / Q000302:isolation & purification; D002118:Calcium / Q000494:pharmacology*; D006801:Humans; D008274:Magnesium / Q000494:pharmacology*; D010767:Phosphorylcholine / Q000494:pharmacology*; D017433:Protein Structure, Secondary / Q000187:drug effects*; D000683:Serum Amyloid P-Component / Q000737:chemistry* / Q000187:drug effects / Q000302:isolation & purification; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
D000683:Serum Amyloid P-Component; D010767:Phosphorylcholine; D002097:C-Reactive Protein; D008274:Magnesium; D002118:Calcium