Atomic resolution structure of a succinimide intermediate in E.coli CheY

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Aspartate isomerization to isoaspartate is a spontaneous post-translational modification in proteins.
• This modification is linked to protein aging and diseases like Alzheimer's.
• The cyclic succinimide intermediate is typically unstable and rarely characterized structurally.

Purpose of the Study:

• To investigate the structural characteristics of the succinimide intermediate during aspartate isomerization.
• To identify factors contributing to the stabilization of this intermediate.
• To understand the impact of succinimide formation on protein structure.

Main Methods:

• X-ray crystallography was used to determine the structure of the Escherichia coli CheY protein.
• The crystal used was eight years old, allowing for the capture of a long-term modification.
• Structural analysis focused on identifying and characterizing the succinimide ring and its interactions.

Main Results:

• An unusually stabilized succinimide ring was discovered in the crystal structure of CheY protein.
• The succinimide ring involved aspartate 75 and glycine 76 in an exposed loop.
• Stabilization was mediated by a sulfate ion interacting with the imide nitrogen.
• Succinimide formation induced local conformational changes in the loop but not the overall protein structure.

Conclusions:

• The study reveals a mechanism for stabilizing the transient succinimide intermediate in protein isomerization.
• This stabilization, facilitated by sulfate ions, provides structural insights into aging-related protein modifications.
• Understanding these stabilized intermediates can inform strategies for mitigating age-related protein damage.