title: Three-dimensional EM structure of the ectodomain of integrin {alpha}V{beta}3 in a complex with fibronectin.
abstract: Integrins are alphabeta heterodimeric cell surface receptors that mediate transmembrane signaling by binding extracellular and cytoplasmic ligands. The ectodomain of integrin alphaVbeta3 crystallizes in a bent, genuflexed conformation considered to be inactive (unable to bind physiological ligands in solution) unless it is fully extended by activating stimuli. We generated a stable, soluble complex of the Mn(2+)-bound alphaVbeta3 ectodomain with a fragment of fibronectin (FN) containing type III domains 7 to 10 and the EDB domain (FN7-EDB-10). Transmission electron microscopy and single particle image analysis were used to determine the three-dimensional structure of this complex. Most alphaVbeta3 particles, whether unliganded or FN-bound, displayed compact, triangular shapes. A difference map comparing ligand-free and FN-bound alphaVbeta3 revealed density that could accommodate the RGD-containing FN10 in proximity to the ligand-binding site of beta3, with FN9 just adjacent to the synergy site binding region of alphaV. We conclude that the ectodomain of alphaVbeta3 manifests a bent conformation that is capable of stably binding a physiological ligand in solution.
authors.affiliation: Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: Brian D
authors.initials: BD
authors.lastname: Adair
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Xiong
authors.forename: Catherine
authors.initials: C
authors.lastname: Maddock
authors.forename: Simon L
authors.initials: SL
authors.lastname: Goodman
authors.forename: M Amin
authors.initials: MA
authors.lastname: Arnaout
authors.forename: Mark
authors.initials: M
authors.lastname: Yeager
mesh_terms: D001665:Binding Sites / Q000502:physiology; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D005353:Fibronectins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D021621:Imaging, Three-Dimensional; D039302:Integrin alphaVbeta3 / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D046911:Macromolecular Substances / Q000737:chemistry / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D011485:Protein Binding / Q000502:physiology; D020836:Protein Structure, Quaternary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology
chemical_list: D005353:Fibronectins; D039302:Integrin alphaVbeta3; D008024:Ligands; D046911:Macromolecular Substances