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Related Experiment Videos

Structural dynamics controls nitric oxide affinity in nitrophorin 4.

Karin Nienhaus1, Estelle M Maes, Andrzej Weichsel

  • 1Department of Biophysics, University of Ulm, Germany.

The Journal of Biological Chemistry
|July 20, 2004
PubMed
Summary

Nitrophorin 4 (NP4) protein in Rhodnius prolixus facilitates nitric oxide (NO) and carbon monoxide (CO) transport. Ligand escape is enhanced in open NP4 conformations but hindered in closed ones, impacting NO reassociation.

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Spectroscopy

Background:

  • Nitrophorin 4 (NP4) transports nitric oxide (NO) in the insect Rhodnius prolixus.
  • NO binds to a ferric iron in NP4's heme plane; carbon monoxide (CO) also binds after iron reduction.

Purpose of the Study:

  • To investigate CO and NO binding and migration in NP4 using spectroscopy.
  • To identify potential ligand docking sites through x-ray crystallography.

Main Methods:

  • Fourier transform infrared spectroscopy at cryogenic temperatures.
  • X-ray cryo-crystallography with xenon.
  • Temperature-derivative spectroscopy and photolysis studies.

Main Results:

  • Multiple IR bands indicate varied active site conformations and hydrophobicity.

Related Experiment Videos

  • Photodissociated CO and NO show narrow IR bands linked to reactive heme iron docking sites.
  • Xenon binding cavities were identified, but no secondary ligand rebinding sites were detected.
  • Efficient NO photoproduct formation occurred in open NP4 conformations, suggesting facilitated ligand escape.

    • Conclusions:

    • Ligand escape from NP4 is conformation-dependent, influenced by active site accessibility and heme iron reactivity.
    • Water may hinder NO reassociation in open conformations, while closed conformations prevent ligand escape.