This is the I-EGF 1 domain found in several integrin betas such as integrin beta 1-7. Structural analysis reveal an epidermal growth factor-like (I-EGF) domains 1 and 2 [1]. EGF1 lacks one disulfide (C2-C4) relative to the integrin EGF 2, 3, and 4 domains, this allows the C-terminal end of EGF1 to flex remarkably relative to its N-terminal end [14].

1: Structural determinants of integrin beta-subunit specificity for latent TGF-beta. Dong X, Hudson NE, Lu C, Springer TA; Nat Struct Mol Biol. 2014;21:1091-1096. PMID:25383667

2: Crystal structure of the extracellular segment of integrin alpha Vbeta3. Xiong JP, Stehle T, Diefenbach B, Zhang R, Dunker R, Scott DL, Joachimiak A, Goodman SL, Arnaout MA; Science. 2001;294:339-345. PMID:11546839

3: Crystal structure of the extracellular segment of integrin alpha Vbeta3 in complex with an Arg-Gly-Asp ligand. Xiong JP, Stehle T, Zhang R, Joachimiak A, Frech M, Goodman SL, Arnaout MA; Science. 2002;296:151-155. PMID:11884718

4: A novel adaptation of the integrin PSI domain revealed from its crystal structure. Xiong JP, Stehle T, Goodman SL, Arnaout MA; J Biol Chem. 2004;279:40252-40254. PMID:15299032

5: Structural basis for distinctive recognition of fibrinogen gammaC peptide by the platelet integrin alphaIIbbeta3. Springer TA, Zhu J, Xiao T; J Cell Biol. 2008;182:791-800. PMID:18710925

6: Structure of a complete integrin ectodomain in a physiologic resting state and activation and deactivation by applied forces. Zhu J, Luo BH, Xiao T, Zhang C, Nishida N, Springer TA; Mol Cell. 2008;32:849-861. PMID:19111664

7: Crystal structure of the complete integrin alphaVbeta3 ectodomain plus an alpha/beta transmembrane fragment. Xiong JP, Mahalingham B, Alonso JL, Borrelli LA, Rui X, Anand S, Hyman BT, Rysiok T, Muller-Pompalla D, Goodman SL, Arnaout MA; J Cell Biol. 2009;186:589-600. PMID:19704023

8: Closed headpiece of integrin alphaIIbbeta3 and its complex with an alphaIIbbeta3-specific antagonist that does not induce opening. Zhu J, Zhu J, Negri A, Provasi D, Filizola M, Coller BS, Springer TA; Blood. 2010;116:5050-5059. PMID:20679525

9: Structure-guided design of a high-affinity platelet integrin alphaIIbbeta3 receptor antagonist that disrupts Mg(2)(+) binding to the MIDAS. Zhu J, Choi WS, McCoy JG, Negri A, Zhu J, Naini S, Li J, Shen M, Huang W, Bougie D, Rasmussen M, Aster R, Thomas CJ, Filizola M, Springer TA, Coller BS; Sci Transl Med. 2012;4:125ra32. PMID:22422993

10: Complete integrin headpiece opening in eight steps. Zhu J, Zhu J, Springer TA; J Cell Biol. 2013;201:1053-1068. PMID:23798730

11: Three-dimensional reconstruction of intact human integrin alphaIIbbeta3: new implications for activation-dependent ligand binding. Choi WS, Rice WJ, Stokes DL, Coller BS; Blood. 2013;122:4165-4171. PMID:24136164

12: alpha(V)beta(3) integrin crystal structures and their functional implications. Dong X, Mi LZ, Zhu J, Wang W, Hu P, Luo BH, Springer TA; Biochemistry. 2012;51:8814-8828. PMID:23106217

13: Structural basis for pure antagonism of integrin alphaVbeta3 by a high-affinity form of fibronectin. Van Agthoven JF, Xiong JP, Alonso JL, Rui X, Adair BD, Goodman SL, Arnaout MA; Nat Struct Mol Biol. 2014;21:383-388. PMID:24658351

14: Leukocyte integrin alphaLbeta2 headpiece structures: The alphaI domain, the pocket for the internal ligand, and concerted movements of its loops. Sen M, Springer TA; Proc Natl Acad Sci U S A. 2016;113:2940-2945. PMID:26936951