DEAMIDATION IN PROTEINS - THE CRYSTAL-STRUCTURE OF BOVINE PANCREATIC RIBONUCLEASE WITH AN ISOASPARTYL RESIDUE AT POSITION-67

The non-enzymatic deamidation of asparagine residues in proteins is a widely occurring reaction, both in vivo and in vitro. Although the imp ortance of this process is commonly recognised, only little structural information is available on it. In order to evaluate the structural e ffects of this reaction in proteins, we have determined the crystal st ructure of a ribonuclease A derivative in which asparagine 67 has been replaced by an isoaspartyl residue, as a consequence of an in vitro d eamidation reaction. The overall structure of the model, refined to a crystallographic R-factor of 0.159 at a resolution of 1.9 Angstrom, is very similar to that of the native protein, but considerable deviatio ns are observed in the region delimited by the disulphide bridge 65-72 . In particular, the insertion of an extra methylene group in the main chain at residue 67 breaks up the hydrogen bond network that makes th is region rater rigid in ribonuclease Angstrom. On the basis of the st ructure observed, some of the slightly but significantly different pro perties of this deamidated derivative, with respect to the native enzy me, can be explained. (C) 1996 Academic Press Limited