title: Capillary electrophoretic study of the binding of zinc(II) ion to bacitracin A1 in water-2,2,2-trifluoroethanol.
abstract: Binding of Zn(2+) to bacitracin A(1) was studied by capillary electrophoresis in water/2,2,2-trifluoroethanol (70/30 v/v) at different apparent pH values in order to estimate the association constant of metal, the acidic dissociation constants and the Stokes radii of both free and bounded peptide in apolar environment. The Stokes radii of the free peptide species were compared with those in aqueous solution, as obtained in a recent study performed by our group, indicating that apolar environment stabilizes bacitracin A(1) in a conformational structure with the lateral chain of apolar amino acids exposed on the external surface. This conformation of the macrocyclic dodecapeptide is ready to interact with Zn(2+) ion, as pointed out by the strong increase of the association constant measured in water/2,2,2-trifluoroethanol with respect to the value obtained in aqueous solution. In addition, whereas Zn(2+) ion binding in aqueous solution provides a sensible reduction of peptide Stokes radius, no sensible variations following to ion binding were observed in hydro-organic solution. The present results suggest that the apolar environment, rather than the metal ion binding, could be responsible for the conformational transition that brings bacitracin A(1) towards its biologically active structure.*
authors.affiliation: Institute of Biochemistry and Clinical Biochemistry, Catholic University of Rome, Rome, Italy. m.castagnola@uniserv.ccr.rm.cnr.it
authors.forename: Massimo
authors.initials: M
authors.lastname: Castagnola
authors.forename: Diana Valeria
authors.initials: DV
authors.lastname: Rossetti
authors.forename: Rosanna
authors.initials: R
authors.lastname: Inzitari
authors.forename: Alberto
authors.initials: A
authors.lastname: Vitali
authors.forename: Alessandro
authors.initials: A
authors.lastname: Lupi
authors.forename: Cecilia
authors.initials: C
authors.lastname: Zuppi
authors.forename: Tiziana
authors.initials: T
authors.lastname: Cabras
authors.forename: Maria Benedetta
authors.initials: MB
authors.lastname: Fadda
authors.forename: Ilaria
authors.initials: I
authors.lastname: Podda
authors.forename: Raffaele
authors.initials: R
authors.lastname: Petruzzelli
authors.forename: Bruno
authors.initials: B
authors.lastname: Giardina
authors.forename: Irene
authors.initials: I
authors.lastname: Messana
mesh_terms: D001414:Bacitracin / Q000737:chemistry*; D019075:Electrophoresis, Capillary / Q000379:methods*; D014270:Trifluoroethanol / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D015032:Zinc / Q000737:chemistry*
chemical_list: D014867:Water; D001414:Bacitracin; D014270:Trifluoroethanol; C026461:bacitracin A; D015032:Zinc