Probing the Ca(2+)-assisted π-π interaction during Ca(2+)-dependent protein folding.

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biophysics

Background:

• Protein folding relies on non-covalent interactions, including cation-π and π-π interactions.
• Theoretical studies suggest cooperativity between cation-π and π-π interactions, but experimental evidence is limited.

Purpose of the Study:

• To experimentally investigate the role of calcium ions in stabilizing protein tertiary structures.
• To characterize the Ca(2+)-binding self-processing module (SPM) of Neisseria meningitidis FrpC.
• To elucidate the mechanism of Ca(2+)-assisted π-π interactions in protein folding.

Main Methods:

• Characterization of a Ca(2+)-binding self-processing module (SPM).
• Analysis of Ca(2+)-induced conformational changes from unstructured to compact fold.
• Investigation of π-π interactions between tryptophan residues and their proximity to the calcium-binding site.

Main Results:

• The SPM undergoes a Ca(2+)-dependent transition to a compact fold.
• This fold is stabilized by a T-shaped π-π interaction between two tryptophan residues.
• The tryptophans are located near the calcium-binding site, indicating Ca(2+)-assisted π-π interaction.

Conclusions:

• The SPM serves as a model for studying Ca(2+)-assisted π-π interactions in protein folding.
• Calcium ions play a crucial role in stabilizing protein tertiary structures through specific non-covalent interactions.
• This finding provides experimental evidence for the interplay between cation-binding and π-π interactions in protein structure stabilization.