Ammonium sensors, insights into a diverse subgroup of the amt-superfamily

Abstract: Ammonium is the most readily available source of nitrogen for all living organisms. Its assimilation is governed by a large, highly conserved protein family whose members can be found in all kingdoms of life1. These ammonium transport proteins (Amt) have evolved to fulfill various roles from environmental ammonium uptake in single cell organisms to ammonium homeostasis and detoxification in plants and animals. Some members can also act as ammonium sensors as described recently in both anammox bacteria and fruit flies2–5. This work focuses on Amt1 from Shewanella denitrificans, another example for ammonium receptors (AmR) that contain a N-terminal Amt domain fused to a C-terminal transducer domain, here a diguanylate cyclase (DGC) domain. The three-dimensional structures of the wild type protein and various functional variants were solved by X-ray crystallography, cryo-electron microscopy and alphafold2 structure prediction. They reveal a rather rigid receptor Amt domain that controls a highly flexible transducer DGC domain through a small HAMP domain6. Solid supported membrane electrophysiology (SSM) experiments on Sd-Amt1 in proteoliposomes showed high-affinity ammonium binding but no transport across the membrane. Finally, the conversion of GTP into the bacterial second messenger cyclic di-GMP by the diguanylate cyclase of Sd-Amt1 was determined by continuous, spectroscopic activity assays. They yielded Michaelis Menten kinetics, insights into product inhibition and the influence of ammonium, and allowed for the analysis of various functional variants. Together, these findings were utilized to propose a potential mechanistic cycle for Sd-Amt1 from protein activation over signal propagation through the protein to its enzymatic activity and reset to the initial resting state

Object Details

• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch
• Notes: Universität Freiburg, Dissertation, 2023

Classification and Topics

• Keyword: Proteine ; Carrier-Proteine ; Rezeptor ; Diguanylate cyclase

Contributors, Places and Time

• Event: Veröffentlichung
• (where): Freiburg
• (who): Universität
• (when): 2023
• Creator: Gschell, Mathias
• Contributor: Andrade, Susana ; Einsle, Oliver ; Albert-Ludwigs-Universität Freiburg. Institut für Biochemie ; Albert-Ludwigs-Universität Freiburg. Fakultät für Chemie und Pharmazie

Further information

• DOI: 10.6094/UNIFR/238699
• URN: urn:nbn:de:bsz:25-freidok-2386999
• Rights: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Last update: 14.08.2025, 10:54 AM CEST