Deprotonation of Glu9 destabilizes the alpha-helix in C-peptide of RNase A.
pK values of Glu2, Glu9, and His12 in the lactone and carboxylate forms of C-peptide at 4.5 and 21 degrees, 0.1 M NACl, have been determined from pH-tritration shifts of n.m.r. signals of the glutamate gamma and histidine ring protons. These have been used in an analysis of the well known pH-induced helix-coil transition in the C-peptide lactone. It has been shown that Glu12 deprotonation results in a twofold increase of the helix content, whereas deprotonation of Glu9 leads to a 28% drop. This latter effect is probably related to Glu-9-His+12 salt bridge formation. The transition within the pH range 5.5-7.5 follows exactly the deprotonation curve of His+12 residue.
Bierzyński
A
A
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw.
D002096:C-Peptide; D005971:Glutamates; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D011487:Protein Conformation; D011522:Protons; D012259:Ribonuclease, Pancreatic
D002096:C-Peptide; D005971:Glutamates; D011522:Protons; D012259:Ribonuclease, Pancreatic