2NPD: An Unusual Twin-his Arrangement In The Pore Of Ammonia Channels Is Essential For Substrate Conductance

Amt proteins constitute a class of ubiquitous integral membrane proteins that mediate movement of ammonium across cell membranes. They are homotrimers, in which each subunit contains a narrow pore through which substrate transport occurs. Two conserved histidine residues in the pore have been proposed to be necessary for ammonia conductance. By analyzing 14 engineered polar and non-polar variants of these histidines, in Escherichia coli AmtB, we show that both histidines are absolutely required for optimum substrate conductance. Crystal structures of variants confirm that substitution of the histidine residues does not affect AmtB structure. In a subgroup of Amt proteins, found only in fungi, one of the histidines is replaced by glutamate. The equivalent substitution in E. coli AmtB is partially active, and the structure of this variant suggests that the glutamate side chain can make similar interactions to those made by histidine.
PDB ID: 2NPDDownload
MMDB ID: 43104
PDB Deposition Date: 2006/10/27
Updated in MMDB: 2006/12
Experimental Method:
x-ray diffraction
Resolution: 2.1  Å
Source Organism:
Similar Structures:
Biological Unit for 2NPD: trimeric; determined by author and by software (PISA,PQS)
Molecular Components in 2NPD
Label Count Molecule
Proteins (3 molecules)
Ammonia Channel(Gene symbol: amtB)
Molecule annotation
Chemicals (6 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB