Structural basis for ligand-regulated oligomerization of AraC

Area of Science:

• Structural biology
• Molecular mechanisms
• Gene regulation

Background:

• The Escherichia coli gene regulatory protein AraC controls arabinose metabolism genes.
• AraC function is modulated by the presence or absence of L-arabinose.
• Understanding AraC's structural dynamics is key to deciphering its regulatory role.

Purpose of the Study:

• To determine the crystal structure of the arabinose-binding and dimerization domain of AraC.
• To elucidate the structural changes upon L-arabinose binding.
• To understand the mechanism of ligand-gated oligomerization and its link to DNA-looping.

Main Methods:

• X-ray crystallography was employed to determine the protein structure.
• Structures were solved at 1.5 angstrom (arabinose-bound) and 2.8 angstrom (uncomplexed) resolution.
• Analysis of structural differences between the bound and unbound states.

Main Results:

• The arabinose-bound AraC exhibits an unusual fold with sugar bound in a beta barrel, fully enclosed by the N-terminal arm.
• Dimerization in the presence of arabinose is mediated by an antiparallel coiled-coil.
• In the absence of arabinose, the N-terminal arm is disordered, exposing the sugar-binding pocket and facilitating oligomerization.

Conclusions:

• Ligand-gated oligomerization is a key feature of AraC structure and function.
• The structural plasticity of AraC allows for modulation of its DNA-binding and regulatory activities.
• This study provides a structural basis for understanding how arabinose controls gene expression in E. coli.