High-Affinity E. coli Methionine ABC Transporter: Structure and Allosteric Regulation

• Published in: Science (American Association for the Advancement of Science) Vol. 321; no. 5886; pp. 250 - 253
• Main Authors: Kadaba, Neena S, Kaiser, Jens T, Johnson, Eric, Lee, Allen, Rees, Douglas C
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 11.07.2008; The American Association for the Advancement of Science
• Subjects: Adenosine triphosphatase; Adenosine triphosphatases; Adenosine Triphosphatases - chemistry; Adenosine Triphosphatases - metabolism; Allosteric Regulation; Amino Acid Sequence; Architecture; ATP binding cassette transporters; ATP-Binding Cassette Transporters - chemistry; ATP-Binding Cassette Transporters - metabolism; Binding Sites; Biochemistry; Biological and medical sciences; Cellular biology; Crystal structure; Crystallography, X-Ray; Cytoplasm; Dimerization; Dimers; E coli; Escherichia coli; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - metabolism; Fundamental and applied biological sciences. Psychology; Hydrolysis; Membrane Transport Proteins - chemistry; Membrane Transport Proteins - metabolism; Methionine - metabolism; Models, Molecular; Molecular biophysics; Molecular Sequence Data; Molybdates; Porters; Protein Conformation; Protein Folding; Protein Structure, Secondary; Protein Structure, Tertiary; Protein Subunits - chemistry; Protein Subunits - metabolism; Structure in molecular biology; Tridimensional structure; Regulation(control); Allosteric regulation; Three dimensional structure; Escherichia coli; Methionine; Bacteria; Affinity; ABC transporter; Enterobacteriaceae; Crystalline structure
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1157987

The crystal structure of the high-affinity Escherichia coli MetNI methionine uptake transporter, a member of the adenosine triphosphate (ATP)-binding cassette (ABC) family, has been solved to 3.7 angstrom resolution. The overall architecture of MetNI reveals two copies of the adenosine triphosphatase (ATPase) MetN in complex with two copies of the transmembrane domain MetI, with the transporter adopting an inward-facing conformation exhibiting widely separated nucleotide binding domains. Each MetI subunit is organized around a core of five transmembrane helices that correspond to a subset of the helices observed in the larger membrane-spanning subunits of the molybdate (ModBC) and maltose (MalFGK) ABC transporters. In addition to the conserved nucleotide binding domain of the ABC family, MetN contains a carboxyl-terminal extension with a ferredoxin-like fold previously assigned to a conserved family of regulatory ligand-binding domains. These domains separate the nucleotide binding domains and would interfere with their association required for ATP binding and hydrolysis. Methionine binds to the dimerized carboxyl-terminal domain and is shown to inhibit ATPase activity. These observations are consistent with an allosteric regulatory mechanism operating at the level of transport activity, where increased intracellular levels of the transported ligand stabilize an inward-facing, ATPase-inactive state of MetNI to inhibit further ligand translocation into the cell.