SEQUENCE-SPECIFIC H-1-NMR ASSIGNMENTS AND SECONDARY STRUCTURE OF A LIPID-ASSOCIATING PEPTIDE FROM HUMAN APOC-I - AN NMR-STUDY OF AN AMPHIPATHIC HELIX MOTIF

The conformation of a synthetic peptide corresponding to residues 35-5 3 (SAKMREWFSETFQKVKEKL) of human apolipoprotein C-I (57 amino acids) w as studied by nuclear magnetic resonance and circular dichroism spectr oscopy in water and in perdeuterated dodecylphosphocholine solution at 37 degrees C and pH 4.8. The proton resonances of the peptide in both solutions were assigned from TOCSY, NOESY and DQF-COSY experiments. I n water solution, the peptide is predominantly ''random'' although nuc lear Overhauser connectivity patterns and H-alpha secondary shifts sho w a threshold population of nascent helical conformers. Upon the addit ion of 40-fold molar excess dodecylphosphocholine to the water solutio n, tire peptide adopts a helical structure that extends throughout the sequence.