Ca2+ selectivity of a chemically modified OmpF with reduced pore volume

Area of Science:

• Biophysics
• Structural Biology
• Molecular Biology

Background:

• Escherichia coli OmpF porin is a channel-forming protein.
• A specific mutant, LECE, possesses a Ca(2+)-binding site and a reactive cysteine residue.

Purpose of the Study:

• To investigate the Ca(2+) selectivity of the LECE mutant after chemical modification.
• To understand the influence of ion binding on channel conductance and cation selectivity.

Main Methods:

• Chemical modification of the LECE mutant using MTSES and glutathione.
• Measurement of ion selectivity using conductance and zero-current potential.
• Theoretical computations using density functional theory and Poisson-Nernst-Planck theory.

Main Results:

• Glutathione modification reduced LECE conductance for Ca(2+), suggesting enhanced Ca(2+) chelation.
• MTSES modification did not significantly alter Ca(2+) conductance.
• Ca(2+) versus monovalent cation selectivity varied with the type of monovalent cation (Li+ vs. Cs+).
• The LECE pore remains permeable to monovalent cations even after Ca(2+) binding.

Conclusions:

• The LECE protein's Ca(2+) binding and selectivity are influenced by chemical modification.
• The pore structure allows for distinct pathways for small, highly charged ions and large ions.
• Computational models support a functional separation of ionic pathways within the pore.