DIRECT NMR MEASUREMENT OF THE FOLDING KINETICS OF A TRIMERIC PEPTIDE

Direct NMR measurements of the folding kinetics are performed on a col lagen-like triple helical peptide. The triple helical peptide was desi gned to model a biologically important region of collagen and has the sequence (POG)(3)ITGARGLAG(POG)(4). Triple helical peptides were synth esized with specifically labeled N-15 amino acid residues in key posit ions, and the kinetics of folding of the individual residues were moni tored directly by measuring the loss of monomer intensity and the incr ease in trimer intensity. The residues at the terminal ends and centra l region could be followed independently and quantitated directly. Res idues located at the terminal ends have rates and kinetics of folding that are distinct from residues in the central region of the peptide. This allows the monitoring of different steps in the folding mechanism and the postulation of the existence of a kinetic intermediate. The N MR data are consistent with a mechanism of association/nucleation and propagation. Hereditary connective tissue diseases are associated with mutations that result in abnormal folding of collagen, and the NMR fo lding experiments on a collagen-like peptide provide a basis for chara cterizing the molecular defect in folding mutations.