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A pore-occluding phenylalanine gate prevents ion slippage through plant ammonium transporters.

ABSTRACT: Throughout all kingdoms of life, highly conserved transport proteins mediate the passage of ammonium across membranes. These transporters share a high homology and a common pore structure. Whether NH3, NH4+ or NH3?+?H+ is the molecularly transported substrate, still remains unclear for distinct proteins. High-resolution protein structures of several ammonium transporters suggested two conserved pore domains, an external NH4+ recruitment site and a pore-occluding twin phenylalanine gate, to take over a crucial role in substrate determination and selectivity. Here, we show that while the external recruitment site seems essential for AtAMT1;2 function, single mutants of the double phenylalanine gate were not reduced in their ammonium transport capacity. Despite an unchanged ammonium transport rate, a single mutant of the inner phenylalanine showed reduced N-isotope selection that was proposed to be associated with ammonium deprotonation during transport. Even though ammonium might pass the mutant AMT pore in the ionic form, the transporter still excluded potassium ions from being transported. Our results, highlight the importance of the twin phenylalanine gate in blocking uncontrolled ammonium ion flux.

SUBMITTER: Ganz P

PROVIDER: S-EPMC6856177 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

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A pore-occluding phenylalanine gate prevents ion slippage through plant ammonium transporters.

Ganz Pascal P Mink Robin R Ijato Toyosi T Porras-Murillo Romano R Ludewig Uwe U Neuhäuser Benjamin B

Scientific reports 20191114 1

Throughout all kingdoms of life, highly conserved transport proteins mediate the passage of ammonium across membranes. These transporters share a high homology and a common pore structure. Whether NH3, NH4+ or NH3 + H+ is the molecularly transported substrate, still remains unclear for distinct proteins. High-resolution protein structures of several ammonium transporters suggested two conserved pore domains, an external NH4+< ...[more]

PMID: 31727964

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Project description:BackgroundMembers of the cation diffusion facilitator (CDF) family are integral membrane divalent cation transporters that transport metal ions out of the cytoplasm either into the extracellular space or into internal compartments such as the vacuole. The spectrum of cations known to be transported by proteins of the CDF family include Zn, Fe, Co, Cd, and Mn. Members of this family have been identified in prokaryotes, eukaryotes, and archaea, and in sequenced plant genomes. CDF families range in size from nine members in Selaginella moellendorffii to 19 members in Populus trichocarpa. Phylogenetic analysis suggests that the CDF family has expanded within plants, but a definitive plant CDF family phylogeny has not been constructed.ResultsRepresentative CDF members were annotated from diverse genomes across the Viridiplantae and Rhodophyta lineages and used to identify phylogenetic relationships within the CDF family. Bayesian phylogenetic analysis of CDF amino acid sequence data supports organizing land plant CDF family sequences into 7 groups. The origin of the 7 groups predates the emergence of land plants. Among these, 5 of the 7 groups are likely to have originated at the base of the tree of life, and 2 of 7 groups appear to be derived from a duplication event prior to or coincident with land plant evolution. Within land plants, local expansion continues within select groups, while several groups are strictly maintained as one gene copy per genome.ConclusionsDefining the CDF gene family phylogeny contributes to our understanding of this family in several ways. First, when embarking upon functional studies of the members, defining primary groups improves the predictive power of functional assignment of orthologous/paralogous genes and aids in hypothesis generation. Second, defining groups will allow a group-specific sequence motif to be generated that will help define future CDF family sequences and aid in functional motif identification, which currently is lacking for this family in plants. Third, the plant-specific expansion resulting in Groups 8 and 9 evolved coincident to the early primary radiation of plants onto land, suggesting these families may have been important for early land colonization.

Dataset Information

A pore-occluding phenylalanine gate prevents ion slippage through plant ammonium transporters.

Publications

A pore-occluding phenylalanine gate prevents ion slippage through plant ammonium transporters.

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