A naturally occurring extracellular alpha-beta clasp contributes to stabilization of beta3 integrins in a bent, resting conformation.
Control of alphaIIb beta3 and alphav beta3 integrin activation is critical for cardiovascular homeostasis. Mutations that perturb association of integrin alpha and beta subunits in their transmembrane and cytoplasmic regions activate the integrin heterodimer, suggesting that a low-affinity or "off" conformation is the default state, likely corresponding to the bent conformation seen in the crystal structure of alphav beta3. In this bent structure, a segment of alphav (301-308) and beta3 (560-567) are juxtaposed. Here we provide evidence that these regions of alphav/alphaIIb and beta3 function as a novel extracellular clasp to restrain activation. Synthetic peptides representing the alphaIIb and beta3 clasp regions promote integrin activation as judged by cell adhesion, cell spreading, and exposure of epitopes for three beta3 LIBS antibodies. Mutation of the clasp region of alphav or beta3 results in a constitutively activated integrin, confirming the role of the extracellular clasp in restraining integrin activation. Molecular dynamics simulations of the alphav beta3 structure yield a refined model for the alphav beta3 clasp and provide plausible explanations for the effects of the activating mutations.
Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, Missouri 63110, USA.
Anthony N
AN
Vomund
Sarah
S
Stuhlsatz-Krouper
Julie
J
Dimitry
Yuhua
Y
Song
William A
WA
Frazier
D001792:Blood Platelets / Q000378:metabolism; D002460:Cell Line; D019281:Dimerization; D006801:Humans; D066298:In Vitro Techniques; D039564:Integrin alphaV / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D039661:Integrin beta3 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020014:K562 Cells; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D040201:Platelet Membrane Glycoprotein IIb / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D039564:Integrin alphaV; D039661:Integrin beta3; D040201:Platelet Membrane Glycoprotein IIb; D011994:Recombinant Proteins