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Cation binding to halorhodopsin.

Sansa Dutta1, Lev Weiner2, Mordechai Sheves1

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|April 25, 2015
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Summary
This summary is machine-generated.

This study reveals that halorhodopsin binds to divalent cations like manganese and calcium. Cation binding affinity is influenced by pH, counterions, and the presence of retinal and bacterioruberin chromophores.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Biophysics

Background:

  • Halorhodopsin is a light-driven chloride pump in the retinal protein family.
  • The Natronomonas pharaonis halorhodopsin mutant strain KM-1 contains retinal and bacterioruberin chromophores.
  • Halorhodopsin possesses chloride binding sites, including site I near the retinal chromophore.

Purpose of the Study:

  • To investigate cation binding to the halorhodopsin mutant strain KM-1.
  • To determine the affinity and characteristics of cation binding to halorhodopsin.

Main Methods:

  • Electron paramagnetic resonance (EPR) spectroscopy was employed to examine cation binding.
  • The study analyzed the effects of pH, counterions, retinal chromophore removal, and bacterioruberin oxidation on cation binding.

Main Results:

  • Divalent cations, specifically Mn(2+) and Ca(2+), were found to bind to halorhodopsin.
  • Halorhodopsin exhibits high affinity for Mn(2+) ions, with binding occurring at multiple sites, including those showing positive cooperativity.
  • Mn(2+) binding is pH-dependent, influenced by counterions, and decreases upon retinal removal or bacterioruberin oxidation.
  • Both Mn(2+) and Cl(-) ions initially bind to sites other than site I, with site I occupancy requiring high anion concentrations.

Conclusions:

  • Halorhodopsin binds to divalent cations, with Mn(2+) showing high affinity.
  • Cation binding is a complex process influenced by various factors, including the protein's chromophores and ionic environment.
  • A synergistic effect between cation and anion binding exists, impacting chloride binding site occupancy.