(A) Structural alignment of A1 and A3 domains colored by sequence similarity (green, identical; blue, similar; tan, dissimilar; and white, aligned to gap). (B) Distance-difference matrix of all aligned backbone atoms. (C) Urea and guanidine hydrochloride denaturation at 25°C monitored by circular dichroism at λ = 222 nm. To see this figure in color, go online.