Complement factor H binds to denatured rather than to native pentameric C-reactive protein.

Binding of the complement regulatory protein, factor H, to C-reactive protein has been reported and implicated as the biological basis for association of the H402 polymorphic variant of factor H with macular degeneration. Published studies utilize solid-phase or fluid-phase binding assays to show that the factor H Y402 variant binds C-reactive protein more strongly than H402. Diminished binding of H402 variant to C-reactive protein in retinal drusen is posited to permit increased complement activation, driving inflammation and pathology. We used well validated native human C-reactive protein and pure factor H Y402H variants to test interactions. When factor H variants were incubated with C-reactive protein in the fluid phase at physiological concentrations, no association occurred. When C-reactive protein was immobilized on plastic, either non-specifically by adsorption in the presence of Ca(2+) to maintain its native fold and pentameric subunit assembly or by specific Ca(2+)-dependent binding to immobilized natural ligands, no specific binding of either factor H variant from the fluid phase was observed. In contrast, both factor H variants reproducibly bound to C-reactive protein immobilized in the absence of Ca(2+), conditions that destabilize the native fold and pentameric assembly. Both factor H variants strongly bound C-reactive protein that was denatured by heat treatment before immobilization, confirming interaction with denatured but not native C-reactive protein. We conclude that the reported binding of factor H to C-reactive protein results from denaturation of the C-reactive protein during immobilization. Differential binding to C-reactive protein, thus, does not explain association of the Y402H polymorphism with macular degeneration.

Aromatic-carbohydrate interactions: an NMR and computational study of model systems.

The interactions of simple carbohydrates with aromatic moieties have been investigated experimentally by NMR spectroscopy. The analysis of the changes in the chemical shifts of the sugar proton signals induced upon addition of aromatic entities has been interpreted in terms of interaction geometries. Phenol and aromatic amino acids (phenylalanine, tyrosine, tryptophan) have been used. The observed sugar-aromatic interactions depend on the chemical nature of the sugar, and thus on the stereochemistries of the different carbon atoms, and also on the solvent. A preliminary study of the solvation state of a model monosaccharide (methyl beta-galactopyranoside) in aqueous solution, both alone and in the presence of benzene and phenol, has also been carried out by monitoring of intermolecular homonuclear solvent-sugar and aromatic-sugar NOEs. These experimental results have been compared with those obtained by density functional theory methods and molecular mechanics calculations.

Theoretical study of inversion and topomerization processes of substituted cyclohexanes: the relevance of the energy 3D hypersurface.

Although the potential energy surface of highly symmetric cyclohexane has been extensively reviewed, no attention has been paid to the study of the effect of substitution of a methylene group by a heteroatom. The substitution may cause changes in molecular symmetry as well as the dipole moment, and the unshared electron pairs associated with the heteroatom may also introduce changes in molecular reactivity. However, these phenomena are not yet completely understood. To address these issues, a rigorous description of the inversion-topomerization process of methylcyclohexane and a revision of the conformational potential energy of oxane and thiane are presented. Moreover, the usefulness of providing a three-dimensional representation of these processes is discussed. In the case of methylcyclohexane, calculations show that three transition states are associated with inversion and four more with topomerization. In contrast, for oxane and thiane, only two transition states are involved with inversion and two with topomerization. Two fundamental conclusions can be drawn from this study. The first is that the inversion process occurs through elementary, stages that we have denoted "conformational elemental stages", which is an analogous term to that used for reaction mechanism description (minima-transition state-minima) where several elemental steps take place. The second conclusion is that two independent processes, inversion and topomerization, are connected by some common conformers. The inversion process controls the ring interchange, while topomerization allows exchange between skewed boats.