tailieunhanh - Báo cáo khoa học: Thermosynechoccus elongatus DpsA binds Zn(II) at a unique three histidine-containing ferroxidase center and utilizes O2 as iron oxidant with very high efficiency, unlike the typical Dps proteins

The cyanobacteriumThermosynechococcus elongatusis one the few bacteria to possess two Dps proteins, DpsA-Te and Dps-Te. The present character-ization of DpsA-Te reveals unusual structural and functional features that differentiate it from Dps-Te and the other known Dps proteins. | Thermosynechoccus elongatus DpsA binds Zn II at a unique three histidine-containing ferroxidase center and utilizes O2 as iron oxidant with very high efficiency unlike the typical Dps proteins Flaminia Alaleona Stefano Franceschini Pierpaolo Ceci Andrea Ilari and Emilia Chiancone . Institute of Molecular Biology and Pathology Department of BiochemicalSciences A. Rossi-Fanelli University of Rome La Sapienza Italy Keywords Dps proteins ferroxidase center ferroxidation reaction protection from reactive oxygen species Thermosynechococcus elongatus Correspondence E. Chiancone Department of Biochemical Sciences A. Rossi-Fanelli University of Rome La Sapienza 00185 Rome Italy Fax 39 06 4440062 Tel 39 06 49910761 E-mail Database The atomic coordinates for DpsA-Te have been deposited in the RCSB Brookhaven Protein Data Bank http under accession code PDB ID 2VXX These authors contributed equally to this work Received 13 October 2009 revised 20 November 2009 accepted 4 December 2009 doi The cyanobacterium Thermosynechococcus elongatus is one the few bacteria to possess two Dps proteins DpsA-Te and Dps-Te. The present characterization of DpsA-Te reveals unusual structural and functional features that differentiate it from Dps-Te and the other known Dps proteins. Notably two Zn II are bound at the ferroxidase center owing to the unique substitution of a metal ligand at the A-site His78 in place of the canonical aspartate and to the presence of a histidine His164 in place of a hydrophobic residue at a metal-coordinating distance in the B-site. Only the latter Zn II is displaced by incoming iron such that Zn II -Fe III complexes are formed upon oxidation as indicated by absorbance and atomic emission spectroscopy data. In contrast to the typical behavior of Dps proteins where Fe II oxidation by H2O2 is about 100-fold faster than by O2 in DpsA-Te the ferroxidation efficiency of O2 is very high and .