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The Structure of a Full-length Membrane-embedded Integrin Bound to a Physiological Ligand
Authors:Aguang Dai  Feng Ye  Dianne W Taylor  Guiqing Hu  Mark H Ginsberg  Kenneth A Taylor
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
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.
Keywords:cell adhesion  electron microscopy (EM)  fibrin  platelet  signal transduction  α  IIbβ  3 integrin  nanodisc
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