Porcine pepsin is a gastric aspartic proteinase that reportedly plays a pivotal role in the\ndigestive process of many vertebrates. We have investigated the three-dimensional (3D) structure\nand conformational transition of porcine pepsin in solution over a wide range of denaturant urea\nconcentrations (0-10 M) using Raman spectroscopy and small-angle X-ray scattering. Furthermore,\n3D GASBOR ab initio structural models, which provide an adequate conformational description\nof pepsin under varying denatured conditions, were successfully constructed. It was shown that\npepsin molecules retain native conformation at 0-5 M urea, undergo partial denaturation at 6 M urea,\nand display a strongly unfolded conformation at 7-10 M urea. According to the resulting GASBOR\nsolution models, we identified an intermediate pepsin conformation that was dominant during the\nearly stage of denaturation. We believe that the structural evidence presented here provides useful\ninsights into the relationship between enzymatic activity and conformation of porcine pepsin at\ndifferent states of denaturation.
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