Negative electrostatic surface potential of protein sites specific for anionic ligands

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biophysics

Background:

• Proteins often utilize complementary electrostatic potentials for substrate binding.
• Anion-binding proteins, like transporters and DNA-binding proteins, are crucial in biological systems.
• The Escherichia coli phosphate receptor (Pst) is a key component of an active transport system.

Purpose of the Study:

• To determine the crystal structure of an active mutant of the E. coli phosphate receptor.
• To calculate and analyze the electrostatic surface potential of the phosphate-binding cleft.
• To investigate the role of electrostatic potential versus hydrogen bonding in anion binding specificity.

Main Methods:

• X-ray crystallography to determine the crystal structure of the T141D mutant phosphate receptor.
• Computational modeling to calculate electrostatic surface potentials for wild-type and mutant receptors.
• Comparative analysis of electrostatic potentials in related proteins (sulfate transporter, DNA-binding protein, redox proteins).

Main Results:

• The phosphate-binding cleft of the E. coli phosphate receptor exhibits an intensely negative electrostatic potential.
• Similar negative potentials were observed in sulfate transport receptors, DNA-binding proteins, and redox proteins.
• Protein-anion interactions relying on hydrogen bonding are not hindered by noncomplementary surface potentials.
• Receptor specificity and affinity are insensitive to charge potential but highly sensitive to unpaired hydrogen bond donors/acceptors.

Conclusions:

• Noncomplementary electrostatic surface potentials do not impede anion binding in proteins that primarily use hydrogen bonding.
• Hydrogen bond network integrity is critical for the specificity and affinity of anion-binding proteins.
• This study reframes the understanding of electrostatic contributions to protein-ligand interactions, particularly for anions.