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Structural basis for Mep2 ammonium transceptor activation by phosphorylation.

Bert van den Berg1, Anupama Chembath1, Damien Jefferies2

  • 1Institute for Cell and Molecular Biosciences, The Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK.

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|April 19, 2016
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Summary

Fungal Mep2 proteins, crucial for ammonium sensing, are inactive and closed when not phosphorylated. Phosphorylation triggers conformational changes, regulating eukaryotic ammonium transport.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Structural Biology

Background:

  • Mep2 proteins are fungal transceptors essential for sensing ammonium and regulating fungal development.
  • The precise molecular mechanisms of Mep2 activity regulation by phosphorylation remain unclear.

Purpose of the Study:

  • To elucidate the structural basis of Mep2 regulation by phosphorylation.
  • To understand how Mep2 functions as an ammonium sensor in eukaryotic systems.

Main Methods:

  • X-ray crystallography was used to determine the structures of Mep2 orthologues from Saccharomyces cerevisiae and Candida albicans.
  • Conformational changes were analyzed by comparing structures under different phosphorylation states (non-phosphorylated vs. phosphorylation-mimicking variants).

Main Results:

  • Non-phosphorylated Mep2 adopts a closed, inactive conformation, occluding the channel exit.
  • Phosphorylation sites are accessible and located away from the channel exit, suggesting allosteric regulation.
  • Phosphorylation-mimicking variants exhibit significant conformational changes in the C-terminal region (CTR).

Conclusions:

  • A model for eukaryotic ammonium transport regulation by Mep2 phosphorylation is proposed.
  • Structural insights reveal how phosphorylation state dictates Mep2 transporter activity.
  • This work clarifies the molecular mechanism of ammonium sensing in fungi.