[Aggregation of C-reactive protein in solutions at acid pH]. / Agregatsiia C-reaktivnogo belka v rastvorakh pri kislom znachenii pH.

The hydrodynamic properties of the C-reactive protein (CRP) at different pH were studied using quasi-elastic light scattering, size-exclusion liquid chromatography, and nonreducing gel electrophoresis. It was shown that a CRP solution at pH 5.0-7.2 presents a polydisperse system the major component of which is the native pentameric CRP. At pH 4.0-4.5, CRP exists in two states having different hydrodynamic properties: the native pentameric form with a molecular mass of 120 kDa and with the hydrodynamic radius of 4.03 nm and high-molecular-weight aggregates with a wide range of their molecular weight distribution. The interaction of the C-reactive protein with monoclonal antibodies to it indicates that conformation-dependent surface epitopes of the protein lose the native structure at pH 5.0-5.5. The aggregation of CRP is an irreversible process, which begins in a narrow pH range of pH 5.0-4.5 and is not accompanied by the dissociation into subunits but is determined by intermolecular interactions of its quasi-native pentamers.

[Hydrodynamic parameters of native C-reactive protein molecule in a solution]. / Gidrodinamicheskie parametry molekuly nativnogo C-reaktivnogo belka v rastvore.

The hydrodynamic properties of the C-reactive protein in solution (pH 6.8) were studied using quasi-elastic light scattering and size-exclusion liquid chromatography. It was shown that the solution containing the C-reactive protein represents a polydisperse system. The values of the translation diffusion coefficient and the apparent molecular weight of the C-reactive protein in solution at pH 6.8 were determined. The values of the translation diffusion coefficient, molecular weight and the hydration radius obtained suggest that the native pentameric C-reactive protein is the major form of the protein in solution at pH 6.8.

[Effect of Ca2+ ions on hydrodynamic properties of pentamer and decamer of C-reactive protein in solution]. / Vliianie ionov Ca2+ na gidrodinamicheskie svoistva pentamera i dekamera C-reaktivnogo belka v rastvore.

The molecular mass and sedimentation coefficient of native C-reactive protein in solution were determined by analytical ultracentrifugation in the presence and absence of calcium ions. Pentameric C-reactive protein was shown to be the major macroscopic form of this protein in solution. The removal of calcium ions from solution caused decompaction of the protein accompanied by changes in its hydrodynamic parameters. The sedimentation coefficient s20(0), w of pentameric C-reactive protein in solution containing 2 mM--Ca2+ (6.6S) exceeded that for C-reactive protein in solution containing 2 mM EDTA (6.4S). Analysis of average molecular masses Mw and Mz obtained from sedimentation data demonstrated that the solution of highly purified protein was not homogeneous. As shown by intermolecular crosslinking, the solution also contained the 241-kDa decamer of C-reactive protein (9.5S) as a separate macroscopic form, whose share hardly reached 10% in the presence of 2 mM Ca2+ and increased after removal of calcium ions. The decamers were shown to result from intermolecular association of the pentamers.