The crystal structure of the Escherichia coli AmtB–GlnK complex reveals how GlnK regulates the ammonia channel

doi:10.1073/pnas.0610348104

The crystal structure of the Escherichia coli AmtB–GlnK complex reveals how GlnK regulates the ammonia channel

*Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom;
^†Department of Molecular Microbiology, John Innes Centre, Norwich NR4 7UH, United Kingdom; and
^‡Biomolecular Research, Paul Scherrer Institut, CH-5232 Villigen, Switzerland

Communicated by Stephen C. Harrison, Harvard Medical School, Boston, MA, November 28, 2006 (received for review November 10, 2006)

Abstract

Amt proteins are ubiquitous channels for the conduction of ammonia in archaea, eubacteria, fungi, and plants. In Escherichia coli, previous studies have indicated that binding of the P_II signal transduction protein GlnK to the ammonia channel AmtB regulates the channel thereby controlling ammonium influx in response to the intracellular nitrogen status. Here, we describe the crystal structure of the complex between AmtB and GlnK at a resolution of 2.5 Å. This structure of P_II in a complex with one of its targets reveals physiologically relevant conformations of both AmtB and GlnK. GlnK interacts with AmtB almost exclusively via a long surface loop containing Y51 (T-loop), the tip of which inserts deeply into the cytoplasmic pore exit, blocking ammonia conduction. Y51 of GlnK is also buried in the pore exit, explaining why uridylylation of this residue prevents complex formation.

Footnotes

^§To whom correspondence should be addressed. E-mail: fritz.winkler{at}psi.ch
Author contributions: M.J.C. and A.D. contributed equally to this work; X.-D.L., P.A.B., F.K.W., and M.M. designed research; M.J.C., A.D., and D.L. performed research; M.J.C., D.L., X.-D.L., and F.K.W. analyzed data; and M.J.C., A.D., P.A.B., F.K.W., and M.M. wrote the paper.
The authors declare no conflict of interest.
Data deposition: The atomic coordinates and structure factors have been deposited in the Protein Data Bank, www.pdb.org (PDB ID code 2NUU).
This article contains supporting information online at www.pnas.org/cgi/content/full/0610348104/DC1.
Abbreviations:

2-OG,

2-oxoglutarate;

CTR,

C-terminal region;

PDB,

Protein Data Bank.