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Updated: Nov 10, 2025
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Analysis of AtHIRD11 Intrinsic Disorder and Binding Towards Metal Ions by Capillary Gel Electrophoresis and Affinity Capillary Electrophoresis
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Unusually Fast bis-Histidyl Coordination in a Plant Hemoglobin
Stefania Abbruzzetti1, Alex J Barker2, Irene Villar3
1Dipartimento di Scienze Matematiche, Fisiche e Informatiche, Università di Parma, Parco Area delle Scienze 7/A, 43124 Parma, Italy.
International Journal of Molecular Sciences
|April 3, 2021
Summary
Medicago truncatula nonsymbiotic hemoglobin (MtGlb1-2) exhibits rapid ligand binding kinetics due to fast histidine dissociation and high association rates. This explains its exceptional reactivity with physiological ligands like oxygen.
Area of Science:
- Biochemistry
- Plant Molecular Biology
- Protein Dynamics
Background:
- Nonsymbiotic hemoglobins in plants play crucial roles in oxygen sensing and metabolism.
- The Medicago truncatula MtGlb1-2 gene produces splice variants with distinct heme domain structures.
Purpose of the Study:
- To elucidate the ligand binding kinetics of MtGlb1-2.1 (two hemes) and MtGlb1-2.4 (one heme) proteins.
- To understand the mechanistic basis for the rapid reactivity of these plant hemoglobins.
Main Methods:
- Femtosecond-nanosecond pump-probe spectroscopy.
- Nanosecond laser flash photolysis.
- Kinetic analysis of ligand rebinding and histidine coordination.
Main Results:
- Unusually fast geminate ligand rebinding within nanoseconds.
- Extremely high rates for distal histidine binding/dissociation from the heme (k ~ 10^5 s^-1).
- High overall ligand binding rate constants, exceeding those of other globins.
Conclusions:
- The rapid ligand binding kinetics are attributed to the high rates of histidine ligation/deligation.
- These unique kinetic properties explain the high reactivity of MtGlb1-2 variants with oxygen, nitric oxide, and nitrite.
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