Recent serpin structures. A, structure of native thermopin (24). The serpin is in green, with the RCL in magenta (part of the RCL is not visible in electron density; the dotted line shows connectivity). The C-terminal sequence is in addition to the serpin domain and folds across the front of β-sheet A. B, structure of native tengpin (26). The serpin is in green, with the RCL in magenta and helix E/s1A in dark blue. The N-terminal sequence (orange coil) is crucial for maintaining the native metastable state. C, structure of PAI-1 in complex with the somatomedin B domain of vitronectin (orange). The serpin is in green, with the RCL in magenta and helix E/s1A in dark blue. D, structure of native TBG in complex with thyroxine (28). The serpin is in green, the RCL is in magenta, and thyroxine is in cyan spheres.