Influence of phosphate ligands in abolishing the conformational difference between ribonuclease A and its acid-denatured derivative.
The initial structural alteration of RNAase A due to acid denaturation (0.5 N HCl, 30 degrees C) that accompanies deamidation (without altering enzymic activity) has been dectected by spectrophotometric titration, fluorescence and ORD/CD measurements. It is shown that acid treated RNAase A has an altered conformation at neutral pH, 25 degrees C. This is characterized by the increased accessibility of buried tyrosine residue(s) towards the solvent. The most altered conformation of RNAase A is found in the 10 h acid-treated derivative. This has about 1.5 additional exposed tyrosine residues and a lesser amount of secondary structure than RNAase A. All three methods (titration, fluorescence and CD) established that the structural transition of RNAase A is biphasic. The first phase occurs within 1 h and the resulting subtle conformational change is constant up to 7 h. Following this, after the release of 0.55 mol of ammonia, the major conformational change begins. The altered conformation of the acid-denatured RNAase A could be reversed completely to the native state through a conformational change induced by substrate analogs like 2'- or 3'-CMP. Thus the monodeamidated derivative isolated from the acid-denatured RNAase A by phosphate is very similar to RNAase A in over-all conformation. The results suggest the possibility of flexibility in the RNAase A molecule that does not affect its catalytic activity, as probed through the tyrosine residues.
D000577:Amides; D002384:Catalysis; D003568:Cytidine Monophosphate / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D010710:Phosphates / Q000494:pharmacology; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation; D012260:Ribonucleases / Q000378:metabolism; D014443:Tyrosine
D000577:Amides; D008024:Ligands; D010710:Phosphates; D014443:Tyrosine; D012260:Ribonucleases; D003568:Cytidine Monophosphate