Abstract
BackgroundPII proteins have a fundamental role in the control of nitrogen metabolism in bacteria, through interactions with different PII targets, controlled by metabolite binding and post-translational modification, uridylylation in most organisms. In the photosynthetic bacterium Rhodospirillum rubrum, the PII proteins GlnB and GlnJ were shown, in spite of their high degree of similarity, to have different requirements for post-translational uridylylation, with respect to the divalent cations, Mg2+ and Mn2+.ResultsGiven the importance of uridylylation in the functional interactions of PII proteins, we have hypothesized that the difference in the divalent cation requirement for the uridylylation is related to efficient binding of Mg/Mn-ATP to the PII proteins. We concluded that the amino acids at positions 42 and 85 in GlnJ and GlnB (in the vicinity of the ATP binding site) influence the divalent cation requirement for uridylylation catalyzed by GlnD.ConclusionsEfficient binding of Mg/Mn-ATP to the PII proteins is required for uridylylation by GlnD. Our results show that by simply exchanging two amino acid residues, we could modulate the divalent cation requirement in the uridylylation of GlnJ and GlnB.Considering that post-translational uridylylation of PII proteins modulates their signaling properties, a different requirement for divalent cations in the modification of GlnB and GlnJ adds an extra regulatory layer to the already intricate control of PII function.
Highlights
PII proteins have a fundamental role in the control of nitrogen metabolism in bacteria, through interactions with different PII targets, controlled by metabolite binding and post-translational modification, uridylylation in most organisms
These proteins exert their role at different levels: they regulate gene expression by modulating the activity of several transcription factors [3], they control the flux through an ammonium transport protein [4] and influence the activity of key metabolic enzymes, e.g. glutamine synthetase (GS) and nitrogenase [5,6]
We have shown that dissociation of the complex formed between GlnJ and the membrane embedded ammonium transport protein AmtB1 is favored by 2-OG and ATP but only in the presence of Mn2+ [13]
Summary
PII proteins have a fundamental role in the control of nitrogen metabolism in bacteria, through interactions with different PII targets, controlled by metabolite binding and post-translational modification, uridylylation in most organisms. Members of the PII family of signal transduction proteins are fundamental molecular messengers involved in the regulation of nitrogen metabolism in bacteria, archaea and eukarya (plants) [1,2]. These proteins exert their role at different levels: they regulate gene expression by modulating the activity of several transcription factors [3], they control the flux through an ammonium transport protein [4] and influence the activity of key metabolic enzymes, e.g. glutamine synthetase (GS) and nitrogenase [5,6]. The structure of S. elongatus GlnB provided an explanation for the negative cooperativity observed in the binding of 2-OG, considering that binding of the first 2-OG molecule generates unequal binding sites in the other two subunits [9]
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