NDLI: Pore Mutations in Ammonium Transporter AMT1 with Increased Electrogenic Ammonium Transport Activity*

Content Provider	PubMed Central
Author	Dominique, Loqué Mora, Silvia I. Andrade, Susana L. A. Pantoja, Omar Frommer, Wolf B.
Abstract	AMT/Mep ammonium transporters mediate high affinity ammonium/ammonia uptake in bacteria, fungi, and plants. The Arabidopsis AMT1 proteins mediate uptake of the ionic form of ammonium. AMT transport activity is controlled allosterically via a highly conserved cytosolic C terminus that interacts with neighboring subunits in a trimer. The C terminus is thus capable of modulating the conductivity of the pore. To gain insight into the underlying mechanism, pore mutants suppressing the inhibitory effect of mutations in the C-terminal trans-activation domain were characterized. AMT1;1 carrying the mutation Q57H in transmembrane helix I (TMH I) showed increased ammonium uptake but reduced capacity to take up methylammonium. To explore whether the transport mechanism was altered, the AMT1;1-Q57H mutant was expressed in Xenopus oocytes and analyzed electrophysiologically. AMT1;1-Q57H was characterized by increased ammonium-induced and reduced methylammonium-induced currents. AMT1;1-Q57H possesses a 100× lower affinity for ammonium (Km ) and a 10-fold higher V max as compared with the wild type form. To test whether the trans-regulatory mechanism is conserved in archaeal homologs, AfAmt-2 from Archaeoglobus fulgidus was expressed in yeast. The transport function of AfAmt-2 also depends on trans-activation by the C terminus, and mutations in pore-residues corresponding to Q57H of AMT1;1 suppress nonfunctional AfAmt-2 mutants lacking the activating C terminus. Altogether, our data suggest that bacterial and plant AMTs use a conserved allosteric mechanism to control ammonium flux, potentially using a gating mechanism that limits flux to protect against ammonium toxicity.
Related Links	http://dx.doi.org/10.1074/jbc.m109.020842
Ending Page	24995
Page Count	8
Starting Page	24988
File Format	PDF
ISSN	00219258
e-ISSN	1083351X
Journal	The Journal of Biological Chemistry
Issue Number	37
Volume Number	284
Language	English
Publisher	American Society for Biochemistry and Molecular Biology
Publisher Date	2009-09-11
Access Restriction	Open
Rights Holder	American Society for Biochemistry and Molecular Biology
Subject Keyword	Cell Biology Biochemistry Molecular Biology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Cell Biology Biochemistry Molecular Biology

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