INVESTIGADORES
RASIA Rodolfo Maximiliano
artículos
Título:
Is there a bridging ligand in metal-substituted zinc beta-lactamases? A spectroscopic and theoretical answer
Autor/es:
ESTIU GL; RASIA RM; CRICCO JA; VILA AJ; ZERNER MC
Revista:
INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY
Referencias:
Año: 2002 vol. 88 p. 118 - 132
ISSN:
0020-7608
Resumen:
The spectral features of Co(II)-substituted metallo-beta-lactamases
were analyzed. Nuclear magnetic resonance (NMR) evidence is provided
that shows no magnetic coupling between the two metal ions in
Co(II),Co(II)-betaLII (beta-lactamase II from Bacillus cercus),
suggesting that no bridging ligand connects them, Ultraviolet-visible
(UV-vis) data are rationalized on the basis of semiempirical quantum
chemical calculations of the intermediate neglect of differential
overlap type (ZINDO/S). The binuclear active sites of the enzymes from
B. cereus (betaLII) and B.fragilis (CcrA) were modeled from the protein
data bank (PDB) coordinates, and calculations were performed at the
multireference configuration interaction level. The active site
geometries of these enzymes were examined using the experimental
electronic spectra as a guide. The model which best fits to the
spectroscopic data lacks a bridging solvent molecule, in agreement with
the NMR data. The model could also reproduce spectral changes seen in
the mixed Zn(II),Co(II) adduct. The bands in the visible range are
associated with ligand field transitions at the high-affinity site,
whereas the UV-calculated features originate in ligand-to-metal charge
transfer to the open shell Co(II) in the low-affinity site. These
results indirectly support the hypothesis that the Co(II),Co(II)
derivative of CcrA is also unbridged, in contrast with the structure of
the native zinc enzyme. These results indicate that the existence of a
bridging ligand is not necessary for metallo-beta-lactamase activity,
and that the second zinc ion is not essential for lowering the pK(a) of
the bound water