ATP-binding cassette domain of the histidine and glutamine transporters
HisP and GlnQ are the ATP-binding components of the bacterial periplasmic histidine and glutamine permeases, respectively. Histidine permease is a multi-subunit complex containing the HisQ and HisM integral membrane subunits and two copies of HisP. HisP has properties intermediate between those of integral and peripheral membrane proteins and is accessible from both sides of the membrane, presumably by its interaction with HisQ and HisM. The two HisP subunits form a homodimer within the complex. The domain structure of the amino acid uptake systems is typical for prokaryotic extracellular solute binding protein-dependent uptake systems. All of the amino acid uptake systems also have at least one, and in a few cases, two extracellular solute binding proteins located in the periplasm of Gram-negative bacteria, or attached to the cell membrane of Gram-positive bacteria. The best-studied member of the PAAT (polar amino acid transport) family is the HisJQMP system of S. typhimurium, where HisJ is the extracellular solute binding proteins and HisP is the ABC protein.
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