A Cytosolic Trans-Activation Domain Essential for Ammonium Uptake

Nature. 2007 Mar 8;446(7132):195-8. doi: 10.1038/nature05579. Epub 2007 Feb 11.

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) suggests that the C terminus interacts physically with cytosolic loops of the neighbouring subunit. Phosphorylation of conserved sites in the C terminus 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Allosteric Regulation
  • Arabidopsis / cytology
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Archaeoglobus fulgidus / chemistry
  • Biological Transport
  • Cation Transport Proteins / chemistry*
  • Cation Transport Proteins / genetics
  • Cation Transport Proteins / metabolism*
  • Conserved Sequence / genetics
  • Cytosol / chemistry*
  • Models, Molecular
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism
  • Mutation / genetics
  • Plant Proteins / chemistry*
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Protein Structure, Tertiary
  • Protein Subunits / chemistry
  • Protein Subunits / genetics
  • Protein Subunits / metabolism
  • Quaternary Ammonium Compounds / metabolism*
  • Transcriptional Activation*

Substances

  • Cation Transport Proteins
  • Multiprotein Complexes
  • Plant Proteins
  • Protein Subunits
  • Quaternary Ammonium Compounds
  • ammonium transporters, plant