Refined structures of two insertion/deletion mutants probe function of the maltodextrin binding protein

Area of Science:

• Structural biology
• Protein biochemistry
• Molecular genetics

Background:

• The maltodextrin binding protein (MalE) from Escherichia coli is crucial for nutrient uptake.
• Understanding structure-function relationships in MalE is key to deciphering transport mechanisms.

Purpose of the Study:

• To elucidate the structural and functional consequences of specific mutations in the Escherichia coli maltodextrin binding protein (MalE).
• To investigate how alterations in hinge regions and peripheral domains affect MalE's interaction with maltose and maltodextrins.

Main Methods:

• X-ray crystallography was employed to determine the three-dimensional structures of two MalE mutants (MalE322 and MalE178) in their maltose-bound states.
• Refinement of the X-ray structures provided detailed atomic-level insights into the protein conformation.

Main Results:

• MalE322, with a mutation in a critical hinge segment, exhibited localized conformational changes and altered transport/growth phenotypes.
• MalE178, with a peripheral domain mutation, remained structurally stable and functionally similar to the wild-type protein.
• Both mutants displayed conservative conformational changes, indicating the protein's inherent stability.

Conclusions:

• Deformation of the hinge strand in MalE322 likely explains its altered biochemical properties.
• The stability and near-wild-type activity of MalE178 are attributed to the mutation's distance from the binding site and conserved interactions.