Gα13 Switch Region 2 Relieves Talin Autoinhibition to Activate αIIbβ3 Integrin.
Integrins function as bi-directional signaling transducers that regulate cell-cell and cell-matrix signals across the membrane. A key modulator of integrin activation is talin, a large cytoskeletal protein that exists in an autoinhibited state in quiescent cells. Talin is a large 235-kDa protein composed of an N-terminal 45-kDa FERM (4.1, ezrin-, radixin-, and moesin-related protein) domain, also known as the talin head domain, and a series of helical bundles known as the rod domain. The talin head domain consists of four distinct lobes designated as F0-F3. Integrin binding and activation are mediated through the F3 region, a critically regulated domain in talin. Regulation of the F3 lobe is accomplished through autoinhibition via anti-parallel dimerization. In the anti-parallel dimerization model, the rod domain region of one talin molecule binds to the F3 lobe on an adjacent talin molecule, thus achieving the state of autoinhibition. Platelet functionality requires integrin activation for adherence and thrombus formation, and thus regulation of talin presents a critical node where pharmacological intervention is possible. A major mechanism of integrin activation in platelets is through heterotrimeric G protein signaling regulating hemostasis and thrombosis. Here, we provide evidence that switch region 2 (SR2) of the ubiquitously expressed G protein (Gα13) directly interacts with talin, relieves its state of autoinhibition, and triggers integrin activation. Biochemical analysis of Gα13shows SR2 binds directly to the F3 lobe of talin's head domain and competes with the rod domain for binding. Intramolecular FRET analysis shows Gα13can relieve autoinhibition in a cellular milieu. Finally, a myristoylated SR2 peptide shows demonstrable decrease in thrombosis in vivo Altogether, we present a mechanistic basis for the regulation of talin through Gα13.
From the Department of Developmental, Molecular, and Chemical Biology.|Sackler School of Graduate Biomedical Sciences, Programs in Cellular and Molecular Physiology.
James
J
Schiemer
From the Department of Developmental, Molecular, and Chemical Biology.
Andrew
A
Bohm
From the Department of Developmental, Molecular, and Chemical Biology.|Pharmacology and Experimental Therapeutics and Molecular Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111.
Li
L
Lin
the Division of Hemostasis and Thrombosis, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02115.
Glenn
G
Merrill-Skoloff
the Division of Hemostasis and Thrombosis, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02115.
Robert
R
Flaumenhaft
the Research Resources Center, Protein Research Laboratory, University of Illinois at Chicago, Chicago, Illinois 60612, and.
Jin-Sheng
JS
Huang
the Department of Pharmacology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612.
Guy C
GC
Le Breton
From the Department of Developmental, Molecular, and Chemical Biology, athar.chishti@tufts.edu.|Sackler School of Graduate Biomedical Sciences, Programs in Cellular and Molecular Physiology.|Pharmacology and Experimental Therapeutics and Molecular Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111.
Athar H
AH
Chishti
D000818:Animals; D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism*; D002448:Cell Adhesion; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D016608:Talin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013927:Thrombosis / Q000378:metabolism / Q000473:pathology; D000099149:Ezrin
D003598:Cytoskeletal Proteins; D044365:GTP-Binding Protein alpha Subunits, G12-G13; D008565:Membrane Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D016608:Talin; D000099149:Ezrin; C071776:radixin
G protein; cytoskeleton; fluorescence resonance energy transfer (FRET); integrin; talin