INCORPORATION OF ACHIRAL PEPTOID-BASED TRIMERIC SEQUENCES INTO COLLAGEN MIMETICS

This report represents initial studies of collagen mimetics with achir al peptoid-based trimeric sequences. The incorporation of achiral unit s into collagen-like structures is of considerable interest for the st ructural simplification of collagen-like biomaterials. The achiral uni t Gly-Nleu-Nleu (where Nleu represents N-isobutylglycine) was position ed between Gly-Pro-Hyp trimeric repeats in collagen-like structures in order to examine the effect of an achiral block on triple helicity. A series of single chain structures, ro-Hyp)(n)-(Gly-Nleu-Nleu)(n)-(Gly -Pro-Kyp)(n)-NH2 (where n = 1-3), and a template-assembled structure, yp)(2)-(Gly-Nleu-Nleu)(2)-(Gly-Pro-Hyp)(2)-NH2](3) (where KTA represen ts cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid), were inve stigated. Biophysical studies were carried out in both H2O and ethylen e glycol (EG)/H2O (2:1, v/v) solvents, using circular dichroism and op tical rotation measurements. Highly cooperative melting curves from op tical rotation determinations were obtained for Ac-(Gly-Pro-Hyp)(n)-(G ly-Nleu-Nieu)(n)- (Gly-Pro-Hyp)(n)-NH2 (n = 2, 3) and p)(2)-(Gly-Nleu- Nleu)(2)-(Gly-Pro-Hyp)(2)-NH2](3), revealing that the achiral trimer c an participate in triple helical structures. These results were also s upported by circular dichroism spectroscopy. For the molecules Pro-Hyp )(3)-(Gly-Nleu-Nleu)(3)(Gly-Pro-Hyp)(3)-NH2 and -[Gly-(Gly-Pro-Hyp)(2) -(Gly-Nleu-Nleu)(2)-NH2](3), the presence of collagen-like structures was also supported by H-1 NMR spectroscopy in H2O. For each structure, a distinct set of resonances, obtained at low temperature, disappeare d once a thermal denaturation temperature was reached. Furthermore, th e analysis of NOE cross-peaks established the close packing of Pro, Hy p, and Nleu. The spatial proximity of Pro and Nleu residues and of Hyp and Nleu residues belonging to different chains was confirmed by mole cular modeling of triple helical ro-Hyp)(3)-(Gly-Nleu-Nleu)(3)-(Gly-Pr o-Hyp)(3)-NH2 .