CONFORMATIONAL STABILITY OF ADRENODOXIN MUTANT PROTEINS

Adrenodoxin and the mutants at the positions T54, H56, D76, Y82, and C 95, as well as the deletion mutants 4-114 and 4-108, were studied by h igh-sensitivity scanning microcalorimetry, limited proteolysis, and ab sorption spectroscopy. The mutants show thermal transition temperature s ranging from 46 to 56 degrees C, enthalpy changes from 250 to 370 kJ /mol, and heat capacity change Delta C-p = 7.28 +/- 0.67 kJ/mol/K, exc ept H56R. The amino acid replacement H56R produces substantial local c hanges in the region around positions 56 and Y82, as indicated by redu ced heat capacity change (Delta C-p = 4.29 +/- 0.37 kJ/mol/K) and enha nced fluorescence. Deletion mutant 4-108 is apparently more stable tha n the wild type, as judged by higher specific denaturation enthalpy an d resistance toward proteolytic degradation. No simple correlation bet ween conformational stability and functional properties could be found .