Unknown

Dataset Information

0

Pore mutations in ammonium transporter AMT1 with increased electrogenic ammonium transport activity.


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 100x lower affinity for ammonium (K(m)) 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.

SUBMITTER: Loque D 

PROVIDER: S-EPMC2757203 | biostudies-literature | 2009 Sep

REPOSITORIES: biostudies-literature

altmetric image

Publications

Pore mutations in ammonium transporter AMT1 with increased electrogenic ammonium transport activity.

Loqué Dominique D   Mora Silvia I SI   Andrade Susana L A SL   Pantoja Omar O   Frommer Wolf B WB  

The Journal of biological chemistry 20090706 37


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 effe  ...[more]

Similar Datasets

| S-EPMC4103351 | biostudies-literature
| S-EPMC4814505 | biostudies-literature
| S-EPMC1852352 | biostudies-literature
| S-EPMC6503033 | biostudies-literature
| S-EPMC2746412 | biostudies-literature
| S-EPMC4002075 | biostudies-literature
| S-EPMC3486016 | biostudies-literature
| S-EPMC1450391 | biostudies-literature
| S-EPMC4465853 | biostudies-literature
| S-EPMC2876029 | biostudies-literature