Fig. 3. SAXS curves for human mini-calpain-5.

(A) Buffer-subtracted averaged scattering curves for 0.75 mg/ml human mini-calpain-5 in with no added Ca²⁺ (blue) and in the presence of 50 mM Ca²⁺ (green) and 50 mM Ca²⁺ with 2 mM leupeptin (red). (B) The linear portion of the Guinier region in the low q region (0.0028 –0.0054 Å⁻¹) such that q.R_g < 1.3 where R_g is 25.7 Å, 23.6 Å and 24.4 Å respectively. (C) The guinier R_g was significantly decreased in the presence of 50 mM Ca²⁺ (green; p ≤ 0.01) and 50 mM Ca²⁺ with 2 mM leupeptin (red; p = ≤ 0.05) (data shown before curve averaging). (D) A similar trend was observed where the addition of 50 mM Ca²⁺ and 50 mM Ca²⁺ with 2 mM leupeptin led to a significant decrease in the D_max (p ≤ 0.01 and ≤ 0.05, respectively). (E) The pairwise distance distribution function P(r) of the averaged data suggests a major change in conformation of the no Ca²⁺ added form on addition of 50 mM Ca²⁺ or 50 mM Ca²⁺ with 2 mM leupeptin.