Mechanism of cis-inhibition of polyQ fibrillation by polyP: PPII oligomers and the hydrophobic effect.
PolyQ peptides teeter between polyproline II (PPII) and beta-sheet conformations. In tandem polyQ-polyP peptides, the polyP segment tips the balance toward PPII, increasing the threshold number of Gln residues needed for fibrillation. To investigate the mechanism of cis-inhibition by flanking polyP segments on polyQ fibrillation, we examined short polyQ, polyP, and tandem polyQ-polyP peptides. These polyQ peptides have only three glutamines and cannot form beta-sheet fibrils. We demonstrate that polyQ-polyP peptides form small, soluble oligomers at high concentrations (as shown by size exclusion chromatography and diffusion coefficient measurements) with PPII structure (as shown by circular dichroism spectroscopy and (3)J(HN-C alpha) constants of Gln residues from constant time correlation spectroscopy NMR). Nuclear Overhauser effect spectroscopy and molecular modeling suggest that self-association of these peptides occurs as a result of both hydrophobic and steric effects. Pro side chains present three methylenes to solvent, favoring self-association of polyP through the hydrophobic effect. Gln side chains, with two methylene groups, can adopt a conformation similar to that of Pro side chains, also permitting self-association through the hydrophobic effect. Furthermore, steric clashes between Gln and Pro side chains to the C-terminal side of the polyQ segment favor adoption of the PPII-like structure in the polyQ segment. The conformational adaptability of the polyQ segment permits the cis-inhibitory effect of polyP segments on fibrillation by the polyQ segments in proteins such as huntingtin.
Darnell
Gregory D
GD
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA.
Derryberry
JohnMark
J
Kurutz
Josh W
JW
Meredith
Stephen C
SC
D002850:Chromatography, Gel; D002942:Circular Dichroism; D004058:Diffusion; D005973:Glutamine / Q000737:chemistry; D006801:Humans; D000071058:Huntingtin Protein; D057927:Hydrophobic and Hydrophilic Interactions; D008956:Models, Chemical; D008958:Models, Molecular; D009419:Nerve Tissue Proteins / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D009687:Nuclear Proteins / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D011073:Polyamines / Q000737:chemistry*; D011487:Protein Conformation; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D013696:Temperature; D044366:Transition Temperature
C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D011073:Polyamines; D005973:Glutamine; C011083:polyproline; C097188:polyglutamine