InterPro: IPR015867 Nitrogen regulatory protein PII/ATP phosphoribosyltransferase, C-terminal

This entry represents a structural domain found in the nitrogen regulatory protein PII, in ATP phosphribosyltransferases (C-terminal domain), and in some bacterial hypothetical proteins. This domain consists of a ferredoxin-like alpha/beta sandwich, which forms trimeric structures with orthogonally packed beta-sheets around a three-fold axis.

PII is a tetrameric protein encoded by glnB that functions as a component of the adenylation cascade involved in the regulation of glutamine synthetase activity [1]. PII helps regulate the level of glutamine synthetase in response to nitrogen source availability. In nitrogen-limiting conditions, PII is uridylylated to form PII-UMP, which allows the deadenylation of glutamine synthetase, thus activating the enzyme. Conversely, in nitrogen excess, PI-UMP is deuridylated to PII, promoting the adenylation and deactivation of glutamine synthetase [2].

ATP phosphoribosyltransferase is the first enzyme of the histidine pathway. It is allosterically regulated, controlling the flow of intermediates through the pathway. The C-terminal domain is the regulatory region of the protein, which binds the allosteric inhibitor histidine [3].