A cytosolic trans-activation domain essential for ammonium uptake

D. Loqué, S. Lalonde, L. L. Looger, N. von Wirén and W. B. Frommer ()
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D. Loqué: Carnegie Institution, 260 Panama St, Stanford, California 94305, USA
S. Lalonde: Carnegie Institution, 260 Panama St, Stanford, California 94305, USA
L. L. Looger: Carnegie Institution, 260 Panama St, Stanford, California 94305, USA
N. von Wirén: Institute for Plant Nutrition, University of Hohenheim, Stuttgart 70593, Germany
W. B. Frommer: Carnegie Institution, 260 Panama St, Stanford, California 94305, USA

Nature, 2007, vol. 446, issue 7132, 195-198

Abstract: Abstract Polytopic membrane proteins are essential for cellular uptake and release of nutrients. To prevent toxic accumulation, rapid shut-off mechanisms are required. Here we show that the soluble cytosolic carboxy terminus of an oligomeric ammonium transporter from Arabidopsis thaliana serves as an allosteric regulator essential for function; mutations in the C-terminal domain, conserved between bacteria, fungi and plants, led to loss of transport activity. When co-expressed with intact transporters, mutants inactivated functional subunits, but left their stability unaffected. Co-expression of two inactive transporters, one with a defective pore, the other with an ablated C terminus, reconstituted activity. The crystal structure of an Archaeoglobus fulgidus ammonium transporter (AMT)1 suggests that the C terminus interacts physically with cytosolic loops of the neighbouring subunit. Phosphorylation of conserved sites in the C terminus2 are proposed as the cognate control mechanism. Conformational coupling between monomers provides a mechanism for tight regulation, for increasing the dynamic range of sensing and memorizing prior events, and may be a general mechanism for transporter regulation.

Date: 2007
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DOI: 10.1038/nature05579

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