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Two functional active conformations of the integrin {alpha}2{beta}1, depending on activation condition and cell type
Gerlinde R Van de Walle1, Karen Vanhoorelbeke, Zsuzsa Majer
1Laboratories for Thrombosis Research, Interdisciplinary Research Centre, Katholieke Universiteit Leuven, Campus Kortrijk, 8500 Kortrijk, Belgium.
The Journal of Biological Chemistry
|August 17, 2005
Summary
The integrin alpha2beta1 exists in three distinct conformational states, influencing cell behavior. This discovery, using antibody IAC-1, reveals new insights into integrin activation and function.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Integrins are crucial cell surface receptors involved in cell adhesion and signaling.
- The integrin alpha2beta1 is a key collagen receptor expressed on platelets and various other cell types.
- Previous research extensively studied conformational states of other integrins, but not alpha2beta1.
Purpose of the Study:
- To investigate and characterize the different conformational states of the integrin alpha2beta1.
- To determine if the integrin alpha2beta1 exhibits multiple conformations similar to other integrins.
- To explore the functional implications of these conformational states in cell adhesion and spreading.
Main Methods:
- Development of a conformation-specific monoclonal antibody, IAC-1, that binds to the activated alpha2beta1.
- Utilizing IAC-1 binding assays in conjunction with collagen binding assays.
- Employing both inside-out signaling stimulation and outside-in manipulation techniques on various cell types, including platelets, Chinese hamster ovary cells, peripheral blood mononuclear cells, and Jurkat cells.
Main Results:
- Demonstrated the existence of three distinct conformational states for integrin alpha2beta1: non-activated, intermediate (collagen-binding only), and fully activated (IAC-1 and collagen-binding).
- Showed that the conformational state of alpha2beta1 is cell-type dependent, with outside manipulation inducing IAC-1 binding in some cell types but not others.
- Revealed that the intermediate conformation, induced by outside manipulation, significantly enhanced cell spreading on collagen compared to other states.
Conclusions:
- Integrin alpha2beta1 exists in at least three distinct conformational states, characterized by differential binding of collagen and the antibody IAC-1.
- The induction and accessibility of these conformational states are influenced by both the cell type and the nature of the stimulus (inside-out vs. outside-in).
- The intermediate conformation of alpha2beta1 plays a functional role in promoting cell adhesion and spreading on collagen-coated surfaces.