Harnessing Environmental Ca²⁺ for Extracellular Protein Thermostabilization

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• Calcium (Ca2+) is abundant, and EF hand motifs bind it in proteins.
• Intracellular EF hand proteins regulate signal transduction via Ca2+-induced conformational changes.
• Extracellular Ca2+ binding's role in protein stability is less understood.

Purpose of the Study:

• Investigate Ca2+ binding to extracellular EF hands.
• Determine if Ca2+ binding confers thermostability.
• Elucidate the conformational coupling mechanisms involved.

Main Methods:

• Studied the extracellular glucose-galactose binding protein (ecGGBP) from E. coli.
• Measured thermostability changes upon Ca2+ binding.
• Utilized statistical thermodynamic analysis of a fluorescently labeled protein conjugate.

Main Results:

• Ca2+ binding to ecGGBP's EF hand increased thermostability by ~17 K.
• Conformational coupling mechanisms in two exchange reactions drive Ca2+-mediated stabilization.
• A disorder-to-order transition in the folded state is crucial for Ca2+-bound state dominance.

Conclusions:

• Extracellular Ca2+ binding stabilizes proteins through conformational coupling.
• This mechanism is shared between thermostabilization and allosteric control in signal transduction.
• Findings suggest evolutionary links between EF hand functions.