Synchrotron Small-Angle X-ray Scattering Studies of the Structure of Porcine Pepsin under Various pH Conditions

作者：Kyeong Sik Jin, Yecheol Rho, Jehan Kim, Heesoo Kim, Ik Jung Kim, Moonhor Ree · 发表于：The Journal of Physical Chemistry B · 年份：2008 · DOI：10.1021/jp805940d · 被引用次数：56 · 研究领域：Protein Interaction Studies and Fluorescence Analysis、Enzyme Structure and Function、Protein Structure and Dynamics

Structural characteristics of various conformational states of porcine pepsin in solution under different pH conditions were investigated in terms of size and shape by small-angle X-ray scattering (SAXS). Low-resolution structural models of porcine pepsin were reconstructed from SAXS data, which were made inside the search volume of maximum dimension (Dmax), calculated from the pair distance distribution function p(r). The reconstructed structural models were obtained without imposing any restrictions on the symmetry or anisometry of the pepsin molecule. Under conditions emulating those for physiological activity of the enzyme, the reconstructed structural models exhibited a more extended C-terminal domain compared to the crystal structure. The differences between the solution and crystal structures of pepsin can be explained by inherent conformations of the flexible subdomain in the C-terminal domain under the solution pH conditions. Under mild acidic conditions where the enzyme is inactive, the reconstructed structural models revealed a compact globular conformation similar in overall shape to the crystal structure. These results indicate that the changes in fluorescence and circular dichroism curves observed under acidic conditions could also arise from the inherent conformation of the flexible subdomain, which has a tendency to roll into a sphere in the overall structure, but without affecting the stability of internal structure. Furthermore, the conformational changes in...