Regulation of glutamine synthetase adenylylation and deadenylylation by the enzymatic uridylylation and deuridylylation of the PII regulatory protein

The Story of Glutamine Synthetase Regulation

“…I have not referred to studies carried out in H. Holzer's laboratory in Freiburg, Germany, that were carried out in parallel to those described here and led to similar findings (46 -49) (for reviews by Holzer et al, see also Refs. 19,25,26,50, and 51 for discussions of the relationships between our results and those in Holzer's laboratory). Also, I have not described the results of beautiful experiments by David Eisenberg on the crystal structure of GS (52-54), extending our knowledge of its structure and confirming in many respects the conclusions arrived at from our studies.…”

“…They found that, like GS, the P II protein exists in two forms: (a) an unmodified form that in the presence of glutamine stimulates the adenylylation of GS by interactions at the adenylylation site (ATa) of the ATase and (b) a uridylylated form (P II -UMP) that in the absence of glutamine and in the presence of 2-oxoglutarate stimulates the deadenylylation of GS by interactions at the deadenylylation site (ATd) of ATase (25). This led to further studies by Mangum et al on the role of P II in GS regulation (26) and studies by Garcia and Rhee (27) showing that the uridylylation and deuridylylation of P II is catalyzed by the same uridylyltransferase (UTase). Subsequently, Adler et al (28) obtained a homogeneous preparation of P II and showed that it is a protein of about M r 44,000, which was later shown by other workers to be a trimer (29).…”

Nitrogen Assimilation in Escherichia coli: Putting Molecular Data into a Systems Perspective

“…Mg 2ϩ is the metal ion cofactor for both activities of UTase (127). Deuridylylation of GlnB-UMP is a hydrolytic reaction that results in the release of UMP (127,137). Because this is not a phosphorolytic reaction, like the deadenylylation reaction (Table 4), but rather a hydrolytic reaction (Table 5), the sum of the two UTase reactions is energetically more costly than that of the two ATase reactions.…”

Interpreting the Plastid Carbon, Nitrogen, and Energy Status. A Role for PII?

“…The effect of UTP on this system was revealed when it was found that the PII protein was covalently modified by uridylylation (PII-UMP) on a Tyr residue. Another bifunctional enzyme, uridylyltransferase/removing enzyme (UT/UR), from the PI fraction catalyzed the uridylylation/deuridylylation reactions (Mangum et al, 1973). PII was purified to homogeneity and shown to be a 12-kD protein with a native mass of 44 kD (Adler et al, 1975).…”