CONFORMATIONAL-ANALYSIS OF THE INTERDOMAIN LINKER OF THE CENTRAL HOMOLOGY REGION OF CHLOROPLAST INITIATION-FACTOR IF3 SUPPORTS A STRUCTURALMODEL OF 2 COMPACT DOMAINS CONNECTED BY A FLEXIBLE TETHER

A peptide corresponding to the interdomain linker of chloroplast IF3 h as been synthesized and its structure studied by NMR and CD as a funct ion of temperature and pH, At low temperature and neutral pH the appar ent helical content is 25%. pH and ionic strength dependent CD studies demonstrate that sidechain-sidechain interactions stabilize the struc ture observed at low temperature. The helicity decreases with temperat ure and above 25 degrees C the peptide is less than 15% helical. These results indicate that the peptide has little intrinsic tendency to fo rm helical structure at physiologically relevant temperatures and stro ngly suggests that the linker region is flexible in intact chloroplast IF3. (C) 1998 Federation of European Biochemical Societies.