The Structure of a Full-length Membrane-embedded Integrin Bound to a Physiological Ligand |
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Authors: | Aguang Dai Feng Ye Dianne W Taylor Guiqing Hu Mark H Ginsberg Kenneth A Taylor |
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Institution: | From the ‡Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-4380 and ;§Department of Hematology and Oncology, University of California at San Diego, La Jolla, California 92093-0726 |
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Abstract: | Increased ligand binding to integrin (“activation”) underpins many biological processes, such as leukocyte trafficking, cell migration, host-pathogen interaction, and hemostasis. Integrins exist in several conformations, ranging from compact and bent to extended and open. However, the exact conformation of membrane-embedded, full-length integrin bound to its physiological macromolecular ligand is still unclear. Integrin αIIbβ3, the most abundant integrin in platelets, has been a prototype for integrin activation studies. Using negative stain electron microscopy and nanodisc-embedding to provide a membrane-like environment, we visualized the conformation of full-length αIIbβ3 in both a Mn2+-activated, ligand-free state and a Mn2+-activated, fibrin-bound state. Activated but ligand-free integrins exist mainly in the compact conformation, whereas fibrin-bound αIIbβ3 predominantly exists in a fully extended, headpiece open conformation. Our results show that membrane-embedded, full-length integrin adopts an extended and open conformation when bound to its physiological macromolecular ligand. |
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Keywords: | cell adhesion electron microscopy (EM) fibrin platelet signal transduction α IIbβ 3 integrin nanodisc |
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