Inhibitory complex of the transmembrane ammonia channel, AmtB, and the cytosolic regulatory protein, GlnK, at 1.96 Å

Department of Biochemistry and Biophysics, Genentech Hall, School of Medicine, University of California, 600 16th Street, San Francisco, CA 94158-2517

Contributed by Robert M. Stroud, November 3, 2006 (received for review October 31, 2006)

Abstract

Ammonia conductance is highly regulated. A P_II signal transduction protein, GlnK, is the final regulator of transmembrane ammonia conductance by the ammonia channel AmtB in Escherichia coli. The complex formed between AmtB and inhibitory GlnK at 1.96-Å resolution shows that the trimeric channel is blocked directly by GlnK and how, in response to intracellular nitrogen status, the ability of GlnK to block the channel is regulated by uridylylation/deuridylylation at Y51. ATP and Mg²⁺ augment the interaction of GlnK. The hydrolyzed product, adenosine 5′-diphosphate orients the surface of GlnK for AmtB blockade. 2-Oxoglutarate diminishes AmtB/GlnK association, and sites for 2-oxoglutarate are evaluated.

Footnotes

*To whom correspondence should be addressed. E-mail: stroud{at}msg.ucsf.edu
Author contributions: F.G. and R.M.S. designed research; F.G. and J.O. performed research; F.G. analyzed data; and F.G. and R.M.S. wrote the paper.
The authors declare no conflict of interest.
Data deposition: The atomic coordinates have been deposited in the Protein Data Bank, www.pdb.org (PDB ID code 2NS1).
This article contains supporting information online at www.pnas.org/cgi/content/full/0609796104/DC1.
Abbreviations:

Am,

ammonium cation and ammonia;

2-KG,

2-oxoglutarate;

Amt,

ammonia transporter.