1uvh: Difference between revisions

The structure and function of Mycobacterium smegmatis Dps (DNA-binding, proteins from starved cells) and of the protein studied by Gupta and, Chatterji, in which the C terminus that is used for binding DNA contains a, histidine tag, have been characterized in parallel. The native dodecamer, dissociated reversibly into dimers above pH 7.5 and below pH 6.0, with, apparent pK(a) values of approximately 7.65 and 4.75; at pH approximately, 4.0, dimers formed monomers. Based on structural analysis, the two, dissociation steps have been attributed to breakage of the salt bridges, between Glu(157) and Arg(99) located at the 3-fold symmetry axes and to, protonation of Asp(66) hydrogen-bonded to Lys(36) across the dimer, interface, respectively. The C-terminal tag did not affect subunit, dissociation, but altered DNA binding dramatically. At neutral pH, protonation of the histidine tag promoted DNA condensation, whereas in the, native C terminus, compensation of negative and positive charges led to, DNA binding without condensation. This different mode of interaction with, DNA has important functional consequences as indicated by the failure of, the native protein to protect DNA from DNase-mediated cleavage and by the, efficiency of the tagged protein in doing so as a result of DNA, sequestration in the condensates. Chemical protection of DNA from, oxidative damage is realized by Dps proteins in a multistep iron, oxidation/uptake/mineralization process. Dimers have a decreased, protection efficiency due to disruption of the dodecamer internal cavity, where iron is deposited and mineralized after oxidation at the ferroxidase, center.

1UVH is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Mycobacterium_smegmatis Mycobacterium smegmatis] with FE as [http://en.wikipedia.org/wiki/ligand ligand]. Structure known Active Site: AC1. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1UVH OCA].  

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