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Publication Abstract from PubMed

To get insight on archaeal nitrogen signaling and on haloadaptation of the nitrogen/carbon/energy-signaling protein PII, we determined crystal structures of recombinantly produced GlnK2 from the extreme halophilic archaea Haloferax mediterranei, complexed with AMP or with the PII effectors ADP or ATP, at respective resolutions of 1.49, 1.45 and 2.60 A. A unique trait of these structures was a three-tonged crown protruding from the trimer body convex side, formed by an 11-residue, N-terminal, highly acidic extension that is absent from structurally studied PII proteins. This extension substantially contributed to the very low pI value which is an haloadaptive trait of H.mediterranei GlnK2, and participated in hexamer-forming contacts in one crystal. Similar acidic N-extensions are shown here to be common among PII proteins from halophilic organisms. Additional haloadaptive traits prominently represented in H. mediterranei GlnK2 are a very high ratio of small residues versus large hydrophobic aliphatic residues; and the largest ratio of polar to non-polar exposed surface for any structurally characterized PII protein. The presence of a dense hydration layer in the region between the three T-loops might also be a haloadaptation. Other unique findings revealed by the GlnK2 structure that might have functional relevance are the adoption by its T-loop of a 3-turn alpha helical conformation, perhaps in relation with the GlnK2 ability to directly interact with glutamine synthetase; and the firm binding of AMP, confirmed by biochemical binding studies with ATP, ADP and AMP, raising the possibility that AMP could be an important PII effector at least in Archaea. This article is protected by copyright. All rights reserved.

The structure of a PII signaling protein from a halophilic archaea reveals novel traits and high-salt adaptations.,Palanca C, Pedro-Roig L, Llacer JL, Camacho M, Bonete MJ, Rubio V FEBS J. 2014 Jun 20. doi: 10.1111/febs.12881. PMID:24946894^[4]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.