Figure 1. Structure of human tenascin-C. A, Organization of the tenascin-C molecule. This diagram is adapted from Aukhil et al. (1993). The N termini of three arms are joined to form a trimer, and two trimers are connected via a disulfide bond (S-S) to form a hexamer. Each arm consists of 14 domains with homology to epidermal growth factor (EGF), 8-17 FN-III repeats depending on alternative RNA splicing, and a single fibrinogen (fbg) domain. The universal FN-III repeats (fn1-5 and fn6-8) are present in all tenascin-C splice variants. The largest tenascin-C splice variant contains nine alternatively spliced FN-III repeats (designated A1, A2, A3, A4, B, AD1, AD2, C, and D, or fnA-D), which are missing in the shortest splice variant. B, Crystal structure of universal tenascin-C FN-III domain 3 (fn3). This structure is adapted from Leahy et al. (1992) and consists of six exposed loops and seven strands. The 91 integrin recognition sequence EIDGIELT, which corresponds to the neurite outgrowth-promoting sequence VFDNFVLK in fnD, is highlighted and includes portions of an exposed loop and adjacent strand.