Conformational plasticity of cryptolepain: Accumulation of partially unfolded states in denaturants induced equilibrium unfolding

• Published in: Journal of biotechnology 2007-09, Vol.131 (4), p.404-417
• Main Authors: Pande, Monu, Dubey, Vikash K., Sahu, Vishal, Jagannadham, Medicherla V.
• Format: Article
• Language: English
• Subjects: Anilino Naphthalenesulfonates - metabolism; Biological and medical sciences; Biotechnology; Circular Dichroism; Fundamental and applied biological sciences. Psychology; Guanidine - pharmacology; Hydrogen-Ion Concentration; Intermediate; Molten globule state; Plant Proteins - chemistry; Plant Proteins - metabolism; Protein Conformation - drug effects; Protein Denaturation - drug effects; Protein Folding; Serine proteases; Spectrometry, Fluorescence; Spectrophotometry, Ultraviolet; Stability; Temperature; Thermodynamics; Urea - pharmacology
• ISSN: 0168-1656; 1873-4863
• DOI: 10.1016/j.jbiotec.2007.08.006

pH and chemical denaturant dependent conformational changes of a serine protease cryptolepain from Cryptolepis buchanani are presented in this paper. Activity measurements, near UV, far UV CD, fluorescence emission spectroscopy, and ANS binding studies have been carried out to understand the folding mechanism of the protein in the presence of denaturants. pH and chemical denaturants have a marked effect on the stability, structure, and function of many globular proteins due to their ability to influence the electrostatic interactions. The preliminary biophysical study on cryptolepain shows that major elements of secondary structure are β-sheets. Under neutral conditions the enzyme was stable in urea while GuHCl-induced equilibrium unfolding was cooperative. Cryptolepain shows little ANS binding even under neutral conditions due to more hydrophobicity of β-sheets. Multiple intermediates were populated during the pH-induced unfolding of cryptolepain. Temperature-induced denaturation of cryptolepain in the molten globule like state is non-cooperative, contrary to the cooperativity seen with the native protein, suggesting the presence of two parts, possibly domains, in the molecular structure of cryptolepain, with different stability that unfolds in steps. Interestingly, the GuHCl-induced unfolding of A state (molten globule state) of cryptolepain is unique, as lower concentration of denaturant, not only induces structure but also facilitate transition from one molten globule like state (MG 1) into another (MG 2). The increase of pH drives the protein into alkaline denatured state characterized by the absence of any ANS binding. GuHCl- and urea-induced unfolding transition curves at pH 12.0 were non-coincidental indicating the presence of an intermediate in the unfolding pathway.