TY - JOUR
T1 - Of blood, brains and bacteria, the Amt/Rh transporter family
T2 - Emerging role of Amt as a unique microbial sensor
AU - Tremblay, Pier-Luc
AU - Hallenbeck, Patrick C.
PY - 2009
Y1 - 2009
N2 - Members of the Amt/Rh family of transporters are found almost ubiquitously in all forms of life. However, the molecular state of the substrate (NH3 or NH4+) has been the subject of active debate. At least for bacterial Amt proteins, the model emerging from computational, X‐ray crystal and mutational analysis is that NH4+ is deprotonated at the exterior, conducted through the membrane as NH3, and reprotonated at the cytoplasmic interface. A proton concomitantly is transferred from the exterior to the interior, although the mechanism is unclear. Here we discuss recent evidence indicating that an important function of at least some eukaryotic and bacterial Amts is to act as ammonium sensors and regulate cellular metabolism in response to changes in external ammonium concentrations. This is now well documented in the regulation of yeast pseudohyphal development and filamentous growth. As well, membrane sequestration of GlnK, a PII signal transduction protein, by AmtB has been shown to regulate nitrogenase in some diazotrophs, and nitrogen metabolism in some Gram‐positive bacteria. Formation of GlnK–AmtB membrane complexes might have other, as yet undiscovered, regulatory roles. This possibility is emphasized by the discovery in some genomes of genes for chimeric Amts with fusions to various regulatory elements.
AB - Members of the Amt/Rh family of transporters are found almost ubiquitously in all forms of life. However, the molecular state of the substrate (NH3 or NH4+) has been the subject of active debate. At least for bacterial Amt proteins, the model emerging from computational, X‐ray crystal and mutational analysis is that NH4+ is deprotonated at the exterior, conducted through the membrane as NH3, and reprotonated at the cytoplasmic interface. A proton concomitantly is transferred from the exterior to the interior, although the mechanism is unclear. Here we discuss recent evidence indicating that an important function of at least some eukaryotic and bacterial Amts is to act as ammonium sensors and regulate cellular metabolism in response to changes in external ammonium concentrations. This is now well documented in the regulation of yeast pseudohyphal development and filamentous growth. As well, membrane sequestration of GlnK, a PII signal transduction protein, by AmtB has been shown to regulate nitrogenase in some diazotrophs, and nitrogen metabolism in some Gram‐positive bacteria. Formation of GlnK–AmtB membrane complexes might have other, as yet undiscovered, regulatory roles. This possibility is emphasized by the discovery in some genomes of genes for chimeric Amts with fusions to various regulatory elements.
U2 - 10.1111/j.1365-2958.2008.06514.x
DO - 10.1111/j.1365-2958.2008.06514.x
M3 - Journal article
C2 - 19007411
SN - 0950-382X
VL - 71
SP - 12
EP - 22
JO - Molecular Microbiology
JF - Molecular Microbiology
IS - 1
ER -