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Structural basis for high-affinity volatile anesthetic binding in a natural 4-helix bundle protein.
Renyu Liu1, Patrick J Loll, Roderic G Eckenhoff
1Department of Anesthesia, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Summary
Researchers identified ferritin as a protein that binds inhaled anesthetics like halothane and isoflurane with high affinity. This discovery suggests direct protein interactions may explain anesthetic effects at low doses.
Area of Science:
- Biochemistry
- Structural Biology
- Pharmacology
Background:
- Inhaled anesthetics' precise binding sites on neurotransmitter receptors remain unconfirmed.
- The structural details of anesthetic-protein interactions are largely unknown.
Purpose of the Study:
- To identify and structurally characterize proteins that bind inhaled anesthetics.
- To elucidate the binding mechanism and affinity of inhaled anesthetics to proteins.
Main Methods:
- Screening of soluble proteins containing 4-alpha-helix bundles for anesthetic binding.
- Determination of crystal structures of halothane/apoferritin and isoflurane/apoferritin complexes at 1.75 A resolution.
Main Results:
- Ferritin demonstrated high-affinity binding (K(A) approx 10(5) M(-1)) for both halothane and isoflurane.
- A common binding pocket was identified at the interhelical dimerization interface of ferritin.
- Anesthetic binding did not alter ferritin's structure or B factors.
Conclusions:
- Ferritin serves as a high-affinity binding protein for inhaled anesthetics.
- The findings suggest greater selectivity of protein binding sites than previously assumed.
- Direct protein actions may be responsible for anesthetic effects at sub-surgical concentrations, including loss of awareness.