This domain is found in Integrin alpha-X from humans (ITGAX) and similar proteins predominantly found in vertebrates. ITGAX is a receptor for fibrinogen. This region composed of an immunoglobulin-like domain [1,3].

1: Structure of an integrin with an alphaI domain, complement receptor type 4. Xie C, Zhu J, Chen X, Mi L, Nishida N, Springer TA; EMBO J. 2010;29:666-679. PMID:20033057

2: An internal ligand-bound, metastable state of a leukocyte integrin, alphaXbeta2. Sen M, Yuki K, Springer TA; J Cell Biol. 2013;203:629-642. PMID:24385486

3: 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