RESUMO
The interaction of arsenite with a Cys(3)His (CCHC) zinc finger model (34-51) HIV-1 nucleocapsid protein p7 (NCp7) peptide in the absence and presence of Zn(II) was studied using fluorescence spectroscopy, CD (circular dichroism) and ESI-MS (Electrospray Ionization Mass Spectrometry). We found that arsenic forms different complexes with the free peptide and the zinc finger peptide. In the former case the peptide conformation differed greatly from that of the zinc finger, whereas in the second case a mixed As-Zn-peptide complex was formed with partial preservation of zinc finger conformation. An apparent stability constant was estimated for the mixed As-Zn-peptide complex (K=2083 M(-1) and 442 M(-1) at 25°C and pHs 6 and 7, respectively). Our study also shows that the interaction of arsenic with the CCHC motif is facilitated by glutathione (GSH), through formation of a GS-As-peptide conjugate.
Assuntos
Arsênio , Arsenitos/química , Complexos de Coordenação/química , Fragmentos de Peptídeos/química , Zinco , Produtos do Gene gag do Vírus da Imunodeficiência Humana/química , Sequência de Aminoácidos , Dicroísmo Circular , Glutationa/química , Cinética , Dados de Sequência Molecular , Ligação Proteica , Espectrometria de Fluorescência , Espectrometria de Massas por Ionização por Electrospray , Dedos de ZincoRESUMO
Sb(III) competes with Zn(II) for its binding to the CCHC zinc finger domain of the NCp7 protein of HIV-1, indicating that zinc finger proteins may be targets for antimony-based drugs and thus responsible for their important pharmacological actions.
Assuntos
Antimônio/química , Compostos Organometálicos/química , Dedos de Zinco , Produtos do Gene gag do Vírus da Imunodeficiência Humana/química , Antimônio/farmacologia , Ligação Competitiva , Concentração de Íons de Hidrogênio , Compostos Organometálicos/farmacologia , Relação Estrutura-Atividade , Zinco/química , Zinco/farmacologia , Dedos de Zinco/efeitos dos fármacos , Produtos do Gene gag do Vírus da Imunodeficiência Humana/efeitos dos fármacosRESUMO
The chemical structures of the pentavalent antimonial drugs, meglumine antimonate (MA) and sodium stibogluconate (SSG), were re-evaluated using electrospray ionization mass spectrometry (ESI-MS) and osmolarity measurements. Both MA and SSG were found to contain 1:1, 1:2, 2:2 and 2:3 Sb(V)-ligand complexes. ESI-MS analysis of MA showed negatively-charged 1:1 (m/z 364) and 2:2 (m/z 765) Sb(V)-meglumine complexes, supporting the predominance of zwitterionic species in solution. Our data are consistent with a structure for the 1:2 Sb(V)-meglumine, which differs from that previously postulated, with two positively-charged amino groups and one negatively-charged antimonate group. Instead of the commonly hypothesized structure for SSG, in which two Sb atoms are linked by an oxygen, an alternative structure is proposed, based on the ability of Sb(V)-gluconate complexes to polymerize. MA (or SSG) in concentrated aqueous solutions, such as of MA (or SSG) in its commercial form, is expected to consist mainly of a mixture of 2:2, 2:3 and 2:1 Sb(V)-ligand complexes, as suggested by the 2:1 Sb-to-particle ratio found by osmometry. 1:1 Sb(V)-ligand complexes in MA and SSG are expected to play an important pharmacological role, as suggested by the slow increase of osmolarity of MA solution upon dilution at 37 degrees C (half-time of 20min).