Secondary Structure Forming Propensity Coupled with Amphiphilicity Is an Optimal Motif in a Peptide or Protein for Association with Chaperonin 60 (GroEL)

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Abstract
The interactions of GroEL with six dansyl peptides were investigated by means of our previously established fluorescence binding assay [Hutchinson, J. P., Oldham, T. C., El-Thaher, T. S. H., and Miller, A. D. (1997) J. Chem. Soc., Perkin Trans. 2, 279−288]. Three peptides (AMPH series) were constructed with a hierarchy of α-helix-forming propensities and amphiphilic characteristics. The remaining three peptides (NON-AMPH series) were prepared with a reordered amino acid sequence designed to form peptides of differing non-amphiphilic α-helix-forming propensity. Of these six peptides, two (AMPH+ and NON-AMPH+) were N-capped with an S-form α-helix-inducing template (Ro 47-1615, Hoffmann-La Roche), two (AMPH- and NON-AMPH-) were N-capped with an R-form non-inducing template (Ro 47-1614, Hoffmann-La Roche), and two (AMPHR and NON-AMPHR) were without N-cap modification. This paper describes how the known strength of interaction of an unfolded protein substrate with the molecular chaperone GroEL (Kd micromolar to nanomolar) may be emulated with a single peptide (AMPH+) (apparent Kd 5 nM) which has a high propensity to form an amphiphilic α-helical structure in solution. Secondary structure forming propensity is not, in and of itself, an important contributor to the strength of interaction with GroEL. However, secondary structure forming propensity coupled with amphiphilicity may be sufficient to account for most, if not all, of the interaction strength between GroEL and an unfolded peptide or protein substrate.