In vitro proof of direct regulation of glutamine synthetase by GlnK proteins in the extreme halophilic archaeon Haloferax mediterranei.

Haloferax mediterranei is an extreme halophilic micro-organism belonging to the Archaea domain that was isolated from the Santa Pola solar salterns (Alicante, Spain) in 1983. The biochemistry of the proteins involved in nitrogen metabolism is being studied, but the knowledge of their regulation is very scarce at present. The PII superfamily is constituted by major regulators of nitrogen metabolism, which are widespread in prokaryotic and eukaryotic organisms. These trimeric proteins (12 kDa per subunit) have in Escherichia coli long been known to regulate GS (glutamine synthetase) activity via its adenylyltransferase/adenylyl-removing enzyme and, more recently, to be able to interact directly with this enzyme in methanogenic archaea. We have tested the possible role of PII proteins in the regulation of ammonium assimilation in our model organism and the results clearly indicate that the direct influence of GS by PII proteins can also take place in halophilic archaea, starting with the comprehension of nitrogen regulation in those organisms.