Adhesion of N-methacryloyl-omega-amino acid primers to collagen analyzed by 13C NMR

Previously, we reported that the strength of the interaction between N-methacryloyl-omega-amino acid (NMomegaA) primers and dentinal collagen exhibited a strong correlation with the bond strength of the resin to etched dentin. To determine the pertinent functional groups of the amino acid residues in the dentinal collagen, to which the amide and/or the carboxylic acid groups of the NMomegaAs are adsorbed, we used 13C NMR techniques--primarily through the observation of spin-lattice relaxation times, Ti--to investigate the adsorption characteristics resulting from the interaction of NMomegaAs with a model oligopeptide for collagen, (PPG)5. The addition of NMomegaAs to a collagenous solution resulted in a decrease in the T1 values of the carbonyl carbons attributed to the carboxylic acid of the C-terminal Gly and to the third amide of the N-terminal Pro residues in the (PPG)5 molecule, thus reflecting the formation of hydrogen-bonded interactions.

Adhesion mechanisms of resin to etched dentin primed with N-methacryloyl glycine studied by 13C-NMR

The origin of the pH-dependent bond strength of the resin to etched dentin treated with N-methacryloyl glycine (NMGly) primer was studied by 13C-nuclear magnetic resonance (NMR) including spin-lattice relaxation time, T1, observation. When the dentinal collagen was suspended in the NMGly solution at pH = 1.6, the T1 values of all the carbons attributed to the NMGly species were significantly decreased. This indicated the presence of an interaction between the NMGly and the dentinal collagen. To obtain detailed information of this interaction, the 13C-NMR spectra of the NMGly were measured in the presence of the model compound for the collagen, (Pro-Pro-Gly)5 at pH = 1.7. The 13C-NMR peaks of the carbonyl carbons of the amide and carboxylic acid in the NMGly species shifted to a higher field and the T1 values decreased. Furthermore, when the molar ratio of (Pro-Pro-Gly)5 to NMGly was decreased from 1:1 to 1:3, the T1 values of the carbonyl carbon attributed to the carboxylic acid in the C-terminal Gly residue of the oligopeptide decreased dramatically. It can be construed that this indicated the formation of a hydrogen bond between the amide, -NH and the carboxylic acid of the NMGly species and the carboxylic acid of the C-terminal Gly residue of the oligopeptide.

Perspectives on the synthesis and application of triple-helical, collagen-model peptides

Collagens can be distinguished from other proteins based on their triple-helical structure. Synthetic peptide models have been developed to better understand the triple helix structurally and to evaluate the triple helix as a recognition element for biological processes. Associated triple-helical peptides were first designed and assembled by solid-phase methodology in the late 1960s. Such peptides were used for triple-helical structural characterization by CD, nmr, and ir spectroscopies, and x-ray crystallography, and for studying the structural preferences of hydroxylases. In the late 1970s, methods were developed for covalently linking the three strands of triple-helical peptides. One benefit of "branched" peptides was the enhancement of triple-helical thermal stability. The incorporation of specific collagen sequences into thermally stable synthetic triple helices in the early 1990s has allowed for the mechanistic investigation of collagen-mediated cell adhesion and platelet aggregation. In time, discriminatory therapeutics may result from the continued exploration and further understanding of the biological effects of collagen primary, secondary, and tertiary structures via triple-helical peptide models.

Effects of a structural change in collagen upon binding to conditioned dentin studied by 13C NMR

To develop a better adhesive functional monomer, it is imperative to understand the adhesion mechanisms of the resin to the dentin surface. Bond strength to the decalcified dentin surface pretreated with dentin primer, an aqueous ethanol solution of N-methacryloyl glycine, increases by increasing the water content in the primer. The aqueous primer could increase the thickness of the hybrid layer. The structural change of dentinal collagen with NM alpha A was studied by using a model compound for collagen,--(1Pro-2Pro-3Gly)10--, by 13C nuclear magnetic resonance (NMR). The model compound was aggregated in ethanol but dissociated in water. It was found that NM alpha A effectively dissociated the aggregated model compound in water. The dissociation of decalcified dentin was essential to create a thick hybrid layer that could afford a higher bond strength to dentin.

Solid-phase synthesis and stability of triple-helical peptides incorporating native collagen sequences

A generally applicable solid-phase methodology has been developed for the synthesis of triple-helical polypeptides incorporating native collagen sequences. Three nascent peptide chains are C-terminal linked through one N alpha-amino and two N epsilon-amino groups of Lys, while repeating Gly-Pro-Hyp triplets induce triple helicity. Different protecting group strategies, including several three-dimensionally orthogonal schemes, have been utilized for the synthesis of four homotrimeric triple-helical polypeptides (THPs) of 79-124 residues, three of which incorporate native type IV collagen sequences. Highly efficient assemblies were achieved by 9-fluorenylmethoxycarbonyl (Fmoc) N alpha-amino group protection, in situ 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate mediated couplings, and 1,8-diazabicyclo [5.4.0] undec-7-ene mediated Fmoc group removal. THPs were characterized by Edman degradation sequencing, size-exclusion chromatography, mass spectrometry, reversed-phase high performance liquid chromatography, and CD spectroscopy. THP thermal stabilities ranged from 35 to 59 degrees C, with chain length and Hyp content being the influential factors. Melting temperatures and van't Hoff enthalpies for peptide triple-helical denaturation could be correlated well to Hyp content. The THP synthetic protocol developed here will allow for the study of both structure and biological activity of specific collagen sequences in homotrimeric and heterotrimeric forms.

Two-dimensional NMR assignments and conformation of (Pro-Hyp-Gly)10 and a designed collagen triple-helical peptide

Homonuclear and heteronuclear 2D NMR methods are used to study two triple-helical peptides. One peptide, (POG)10, is considered to be the most stable prototype of a triple helix. The second peptide, (POG)3ITGARGLAGPOG(POG)3 (denoted T3-785), was designed to model an imino acid poor region of collagen and contains 12 residues from near the unique collagenase cleavage site in type III collagen. Both peptides associated as trimers, with melting temperatures of 60 degrees C for (POG)10 and 25 degrees C for the T3-785 peptide. Sequence-specific assignments were made for a tripeptide unit POG in (POG)10, and 80% of the POG triplets are found to be in an equivalent environment. In T3-785, with nonrepeating X-Y-Gly units incorporated in the sequence, the three chains of the homotrimer can be distinguished from one another by NMR. The solution conformation of (POG)10 is very similar to the model derived from X-ray fiber diffraction data, although the peptide contains less ordered regions at the peptide ends. In the trimer from of T3-785, the central residues of the three chains are closely packed, and the data are consistent with a triple-helical model with a one-residue stagger of three parallel chains. For T3-785, in contrast to (POG)10, there are also resonances from a less ordered form, which are probably due to the presence of a small amount of monomer. The similarity of the backbone conformations of T3-785 and (POG)10 suggests that an alternative conformation is not present in the imino acid poor region.