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J. Biol. Chem., Vol. 279, Issue 53, 55202-55210, December 31, 2004

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Complex Formation and Catalytic Activation by the P_II Signaling Protein of N-Acetyl-L-glutamate Kinase from Synechococcus elongatus Strain PCC 7942^*

Mani Maheswaran, Claus Urbanke¶, and Karl Forchhammer||

From the Institut für Mikrobiologie und Molekularbiologie, Justus-Liebig Universität Giessen, Heinrich-Buff-Ring 26-32, D-35392 Giessen and ^¶Zentrale Einrichtung für Biophysikalisch-Biochemische Verfahren, Medizinische Hochschule Hannover, Carl Neuberg Strasse 1, D-30623 Hannover, Germany

The signal transduction protein P_II from the cyanobacterium Synechococcus elongatus strain PCC 7942 forms a complex with the key enzyme of arginine biosynthesis, N-acetyl-L-glutamate kinase (NAGK). Here we report the effect of complex formation on the catalytic properties of NAGK. Although pH and ion dependence are not affected, the catalytic efficiency of NAGK is strongly enhanced by binding of P_II, with K_m decreasing by a factor of 10 and V_max increasing 4-fold. In addition, arginine feedback inhibition of NAGK is strongly decreased in the presence of P_II, resulting in a tight control of NAGK activity under physiological conditions by P_II. Analysis of the NAGK-P_II complex suggests that one P_II trimer binds to one NAGK hexamer with a K_d of 3 nM. Complex formation is strongly affected by ATP and ADP. ADP is a strong inhibitor of complex formation, whereas ATP inhibits complex formation only in the absence of divalent cations or in the presence of Mg²⁺ ions, together with increased 2-oxoglutarate concentrations. Ca²⁺ is able to antagonize the negative effect of ATP and 2-oxoglutarate. ADP and ATP exert their adverse effect on NAGK-P_II complex formation through binding to the P_II protein.

Received for publication, September 23, 2004 , and in revised form, October 20, 2004.

^* This work was supported by Deutsche Forschungsgemeinschaft Grant Fo 195/4. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Fellow of the Deutscher Akademischer Austausch Dienst International Quality Network at the University of Giessen and Graduiertenkolleg 370.

^|| To whom correspondence should be addressed. Tel.: 49-641-9935545; Fax: 49-641-9935549; E-mail: Karl.Forchhammer{at}mikro.bio.uni-giessen.de.

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