Related Experiment Video
Updated: Jul 3, 2026
09:35
Real Time Measurements of Membrane Protein:Receptor Interactions Using Surface Plasmon Resonance (SPR)
Published on: November 29, 2014
The high-affinity E. coli methionine ABC transporter: structure and allosteric regulation
Neena S Kadaba1, Jens T Kaiser, Eric Johnson
1Howard Hughes Medical Institute and Division of Chemistry and Chemical Engineering, Mail Code 114-96, California Institute of Technology, Pasadena, CA 91125, USA.
Science (New York, N.Y.)
|July 16, 2008
Summary
The crystal structure of the Escherichia coli MetNI transporter reveals how methionine binding inhibits its function. This discovery explains the allosteric regulation of this essential amino acid uptake system.
Area of Science:
- Structural Biology
- Biochemistry
- Molecular Biology
Background:
- The Escherichia coli MetNI transporter is a key component of the adenosine triphosphate (ATP)-binding cassette (ABC) family, responsible for methionine uptake.
- Understanding the structural basis of ABC transporter function is crucial for elucidating cellular transport mechanisms.
Purpose of the Study:
- To determine the high-resolution crystal structure of the MetNI methionine transporter.
- To elucidate the mechanism of allosteric regulation of methionine transport.
Main Methods:
- X-ray crystallography was used to solve the crystal structure of MetNI at 3.7 angstrom resolution.
- Biochemical assays were performed to investigate the effect of methionine binding on ATPase activity.
Main Results:
- The crystal structure revealed an inward-facing conformation with separated nucleotide binding domains.
- Methionine was found to bind to the carboxyl-terminal domain of MetN, inhibiting ATPase activity.
- The structure highlights a unique regulatory mechanism involving carboxyl-terminal extensions.
Conclusions:
- The MetNI transporter functions via an allosteric regulatory mechanism.
- High intracellular methionine levels stabilize an inactive inward-facing conformation, inhibiting further transport.
- This structural insight provides a molecular basis for understanding methionine homeostasis in E. coli.
Related Concept Videos
01:31ABC Transporters: Exporter
ATP-binding cassette or ABC transporter is the largest superfamily of integral membrane proteins. The transporters have transmembrane-binding domains (TMDs) and nucleotide-binding domains (NBDs). The TMDs are specific to their substrates, whereas the NBDs are similar to engines that complete ATP hydrolysis to complete the substrate transport. They can be full transporters consisting of two TMDs and NBDs, half transporters with one TMD and NBD, while some encoded with a single TMD or NBD are...
01:27ABC Transporters: Importer
ATP-binding cassette or ABC transporters are a class of ATP-driven pumps that hydrolyze ATP to move solutes across the membrane. They can be grouped into importers and exporters. While exporters are present in all domains of life, importers exist only in bacteria and some plants.
In bacteria, based on the number of transmembrane helices and the chemical nature of their substrates, the ABC importers can be divided into three types:
In bacteria, based on the number of transmembrane helices and the chemical nature of their substrates, the ABC importers can be divided into three types:
01:08Allosteric Regulation
Allosteric regulation of enzymes occurs when the binding of an effector molecule to a site that is different from the active site causes a change in the enzymatic activity. This alternate site is called an allosteric site, and an enzyme can contain more than one of these sites. Allosteric regulation can either be positive or negative, resulting in an increase or decrease in enzyme activity. Most enzymes that display allosteric regulation are metabolic enzymes involved in the degradation or...
01:08Allosteric Regulation
Allosteric regulation of enzymes occurs when the binding of an effector molecule to a site that is different from the active site causes a change in the enzymatic activity. This alternate site is called an allosteric site, and an enzyme can contain more than one of these sites. Allosteric regulation can either be positive or negative, resulting in an increase or decrease in enzyme activity. Most enzymes that display allosteric regulation are metabolic enzymes involved in the degradation or...
01:19Allosteric Proteins-ATCase
Binding sites linkages can regulate a protein's function. For example, enzyme activity is often regulated through a feedback mechanism where the end product of the biochemical process serves as an inhibitor.
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...
01:58Cooperative Allosteric Transitions
Cooperative allosteric transitions can occur in multimeric proteins, where each subunit of the protein has its own ligand-binding site. When a ligand binds to any of these subunits, it triggers a conformational change that affects the binding sites in the other subunits; this can change the affinity of the other sites for their respective ligands. The ability of the protein to change the shape of its binding site is attributed to the presence of a mix of flexible and stable segments in the...