Publication Date:
2012-03-13
Description:
Food-borne hemorrhagic Escherichia coli, exemplified by the strains O157:H7 and O104:H4 (refs 1, 2), require elaborate acid-resistance systems (ARs) to survive the extremely acidic environment such as the stomach (pH approximately 2). AR2 expels intracellular protons through the decarboxylation of L-glutamate (Glu) in the cytoplasm and exchange of the reaction product gamma-aminobutyric acid (GABA) with extracellular Glu. The latter process is mediated by the Glu-GABA antiporter GadC, a representative member of the amino-acid-polyamine-organocation superfamily of membrane transporters. The functional mechanism of GadC remains largely unknown. Here we show, with the use of an in vitro proteoliposome-based assay, that GadC transports GABA/Glu only under acidic conditions, with no detectable activity at pH values higher than 6.5. We determined the crystal structure of E. coli GadC at 3.1 A resolution under basic conditions. GadC, comprising 12 transmembrane segments (TMs), exists in a closed state, with its carboxy-terminal domain serving as a plug to block an otherwise inward-open conformation. Structural and biochemical analyses reveal the essential transport residues, identify the transport path and suggest a conserved transport mechanism involving the rigid-body rotation of a helical bundle for GadC and other amino acid antiporters.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ma, Dan -- Lu, Peilong -- Yan, Chuangye -- Fan, Chao -- Yin, Ping -- Wang, Jiawei -- Shi, Yigong -- England -- Nature. 2012 Mar 11;483(7391):632-6. doi: 10.1038/nature10917.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Ministry of Education Protein Science Laboratory, Center for Structural Biology, Tsinghua University, Beijing 100084, China.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22407317" target="_blank"〉PubMed〈/a〉
Keywords:
Antiporters/*chemistry/*metabolism
;
Biological Transport
;
Crystallography, X-Ray
;
Escherichia coli O157/*chemistry
;
Escherichia coli Proteins/*chemistry/*metabolism
;
Glutamic Acid/*metabolism
;
Membrane Proteins/*chemistry/*metabolism
;
Models, Molecular
;
Protein Structure, Tertiary
;
Proteolipids/metabolism
;
Rotation
;
Structure-Activity Relationship
;
gamma-Aminobutyric Acid/*metabolism
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
