Analysis of the conformational transitions of proteins by temperature-gradient gel electrophoresis

Temperature‐gradient gel electrophoresis (TGGE) is a technique for studying the structural transitions of nucleic acids and proteins. A temperature gradient is formed in a horizontal slab gel perpendicular to the direction of the electric field. Whereas the principle of the TGGE method has previously been applied to proteins, we describe in this report the systematic optimization of TGGE as a routine technique for the quantitative analysis of conformational transitions in proteins. Using α‐amylase as an example we show the kinds of results which may be obtained from such measurements. Buffers suitable for use in gel electrophoresis were analyzed with respect to the dependence of their pH value upon temperature. The correct pH range for TGGE of a given protein is determined by electrophoretic titration curves. The protein bands are detected by silver and/or activity staining. The thermal denaturation of α‐amylase from Aspergillus oryzae showed a discontinuous transition into the denatured conformation, which exhibited much slower electrophoretic mobility. The discontinuity is due to an irreversible denaturation process under the gel conditions. The transition temperature was measured as a function of several parameters, e. g., the concentration of Ca++, dithiotreithol, urea and the pH value. The structural transition of α‐amylase is accompanied by a loss of enzymatic activity as determined by activity staining or by an activity assay carried out in solution. The structural transitions of two other α‐amylases from Bacillus subtilis and Bacillus licheniformis were also studied. The results show that the TGGE method is simple to perform and allows the analysis of conformational transitions of proteins in a wide variety of conditions. It is also possible to analyze the conformational stability of proteins in unpurified extracts if activity‐ or immuno‐tests are used for detection.