Heparin influence on alpha-staphylotoxin formed channel

Area of Science:

• Biophysics
• Molecular Biology
• Membrane Protein Studies

Background:

• Staphylococcus aureus alpha-toxin (ST channel) forms pores in lipid bilayers.
• Understanding ion channel gating mechanisms is crucial for pharmacology and disease research.

Purpose of the Study:

• To investigate the effects of heparin on the voltage sensitivity of ST channels.
• To elucidate the molecular interactions governing heparin-ST channel modulation.

Main Methods:

• Voltage clamp electrophysiology on lipid bilayers reconstituted with ST channels.
• Dose-response studies with varying heparin concentrations.
• Investigation of divalent cation effects (Zn2+, Ca2+, Mg2+).

Main Results:

• Low heparin concentrations (100 pM) induced a dose-dependent increase in ST channel voltage sensitivity.
• Heparin's effect was dependent on its addition to the negative-potential side and the presence of divalent cations.
• Divalent cation efficiency followed the order Zn2+ > Ca2+ > Mg2+.
• Apparent positive gating charge increased 2-3 fold with heparin or acidification.
• The cis mouth of the channel showed less sensitivity to heparin than the trans mouth.

Conclusions:

• Heparin, in conjunction with divalent cations, modulates ST channel gating by interacting with charged residues.
• Divalent cations act as bridges between heparin's sulfate groups and the protein's carboxyl groups.
• Charged residues at the cis and trans mouths of the ST channel likely differ in their interaction with heparin.