ABSTRACT
Protein-DNA interactions are highly dependent on salt concentration. To gain insight into how such interactions are maintained in the highly saline cytoplasm of halophilic archaea, we determined the 3-D structure of VNG0258H/RosR, the first haloarchaeal DNA-binding protein from the extreme halophilic archaeon Halobactrium salinarum. It is a dimeric winged-helix-turn-helix (wHTH) protein with unique features due to adaptation to the halophilic environment. As ions are major players in DNA binding processes, particularly in halophilic environments, we investigated the solution structure of the ionic envelope and located anions in the first shell around the protein in the crystal using anomalous scattering. Anions that were found to be tightly bound to residues in the positively charged DNA-binding site would probably be released upon DNA binding and will thus make significant contribution to the driving force of the binding process. Unexpectedly, ions were also found in a buried internal cavity connected to the external medium by a tunnel. Our structure lays a solid groundwork for future structural, computational and biochemical studies on complexes of the protein with cognate DNA sequences, with implications to protein-DNA interactions in hyper-saline environments.
Subject(s)
Archaeal Proteins/chemistry , Archaeal Proteins/metabolism , DNA-Binding Proteins/chemistry , DNA-Binding Proteins/metabolism , Amino Acid Sequence , Crystallography, X-Ray , Halobacterium salinarum , Molecular Sequence Data , Protein Structure, SecondaryABSTRACT
A curious fusion between chlorite dismutase-like and antibiotic biosynthesis monooxygenase-like domains within a single open reading frame has been revealed by both sequence homology and structural modeling in Haloferax volcanii PitA and its homologues in other halophilic archaea. While this fusion may reflect an environmental adaptation to life in hypersaline environments and hence one specific to haloarchaea, PitA and its homologues may represent a paradigm of biologically-relevant interplay between these two distinct activities in accordance with the Rosetta Stone approach.
