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Energetics of leukocyte integrin activation
1Laboratory of Cellular Physiology and Immunology, Rockefeller University, New York, New York 10021, USA.
The Journal of Biological Chemistry
|June 16, 1995
Summary
Leukocyte integrin CR3 (CD11b/CD18) binding is not driven by affinity changes. Instead, activation and ligand detachment involve distinct energy-dependent steps, impacting cell adhesion.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Leukocyte integrin CR3 (CD11b/CD18) mediates cell adhesion.
- Adhesion is thought to be regulated by reversible changes in CR3's affinity for its ligand.
- Understanding CR3's binding mechanism is crucial for immune response research.
Purpose of the Study:
- To investigate the binding affinity of the leukocyte integrin CR3.
- To determine the mechanism regulating CR3-mediated cell adhesion.
- To elucidate the role of receptor activation and ligand binding/detachment.
Main Methods:
- Purified active and inactive CR3 receptor were used.
- Binding affinity was measured using the ligand C3bi coupled to alkaline phosphatase.
- The effect of the activating antibody KIM-127 on CR3 binding was assessed.
Main Results:
- Active CR3 bound C3bi with high affinity (12.5 +/- 4.7 nM).
- Inactive CR3 showed no measurable binding.
- The antibody KIM-127 facilitated binding by lowering activation energy, not by altering affinity.
Conclusions:
- CR3-mediated cell adhesion and detachment are not driven by reversible affinity changes.
- Binding involves an energetically neutral activation step.
- Detachment requires an energy-dependent step, suggesting distinct regulatory processes.