Model of the Ca⁺⁺-binding loops and C-terminal sequence of TSP-1 and positions of reactive cysteine.

Small circles represent the relative positions of the 19 cysteines in the Ca⁺⁺-binding loops and C-terminal sequence. Open circles, shaded circles, and solid circles represent cysteines not involved in disulfide exchange, moderately involved in disulfide exchange, and heavily involved in disulfide exchange, respectively, in Ca⁺⁺-depleted TSP-1.26 In TSP-1 purified in buffers containing 0.1 mM Ca⁺⁺,27 as well as in E3CaG-1, the free thiol is at Cys974. The dotted lines represent the likely disulfide bonding based on the disulfide connectivity of E3CaG-2.17 Cys974 may exchange with Cys928 or Cys892 (arrows).