The structure of the Ce(III)-angiotensin II complex as obtained from NMR data and molecular dynamics calculations

Effect of Cu(II) on the complex between kanamycin A and the bacterial ribosomal A site

The solution structure of kanamycin A interacting with a ribosomal A-site fragment was solved by transferred-NOE techniques and found to agree with the structure of the complex observed in the crystal. Despite the fast exchange conditions found for the interaction, the bound form was identified by NOESY spectroscopy. At 600 MHz, NOE effects are only observed for the RNA-associated antibiotic. Dissociation constants were measured by NMR spectroscopy for two sites of interaction (K(d1)=150+/-40 microM; K(d2)=360+/-50 microM). Furthermore, the effects of the Cu(II) ion on the antibiotic, on the RNA fragment that mimics the bacterial ribosomal A site, and on the complex formed between these two entities were analyzed. The study led to the proposal of a model that localizes the copper ion within the kanamycin-RNA complex.

1H and 13C-NMR and molecular dynamics studies of cyclosporin a interacting with magnesium(II) or cerium(III) in acetonitrile. Conformational changes and cis-trans conversion of peptide bonds

Cyclosporin A (CsA) is an important drug used to prevent graft rejection in organ transplantations. Its immunosuppressive activity is related to the inhibition of T-cell activation through binding with the proteins Cyclophilin (Cyp) and, subsequently, Calcineurin (CN). In the complex with its target (Cyp), CsA adopts a conformation with all trans peptide bonds and this feature is very important for its pharmacological action. Unfortunately, CsA can cause several side effects, and it can favor the excretion of calcium and magnesium. To evaluate the possible role of conformational effects induced by these two metal ions in the action mechanism of CsA, its complexes with Mg(II) and Ce(III) (the latter as a paramagnetic probe for calcium) have been examined by two-dimensional NMR and relaxation rate analysis. The conformations of the two complexes and of the free form have been determined by restrained molecular dynamics calculations based on the experimentally obtained metal-proton and interproton distances. The findings here ratify the formation of 1:1 complexes of CsA with both Mg(II) and Ce(III), with metal coordination taking place on carbonyl oxygens and substantially altering the peptide structure with respect to the free form, although the residues involved and the resulting conformational changes, including cis-trans conversion of peptide bonds, are different for the two metals.