Pii nitrogen regulatory proteins

The Nitrogen regulatory protein P-II family contains a series of homologous prokaryotic signalling proteins which are involved in the regulation of nitrogen metabolism. The proteins are post translationally modified via addition of a uridylyl group by the enzyme Uridylyltransferase. The presence or absence of this group modulates the behaviour of the protein. In turn, uridylation is controlled by cellular levels of alpha=ketoglutarate and ATP.

PII proteins exist in trimers in vivo and bind ATP in a cleft between the subunits. There are two flexible loops call the B-loop and T-loop which are involved in regulation of the protein. The T-loop contains a conserved tyrosine which is the site of uridyl attachment.

Following nitrogen starvation, increased intra-cellular concentrations of ammonia cause the de-uridylylation of GlnK. This then binds directly to the ammonia channel AmtB to block ammonia conduction.