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Research reveals that amino acid propensity analysis of collagen triple-helix show highly stabilizing nature of imino acids and destabilization by glycine and aromatic residues. Data demonstrate that the capacity of amino acids to adopt a polyproline II-like conformation influence collagen's triple-helix ranking.

Research suggests that the local triple-helical dynamics or structure of type III collagen may be modulated by Gly-Gly-Y triplets. Triple-helical peptides' thermal stability is lowered through the influence exerted by the Gly-Gly-Y triplets next to the epitope, with the tripeptides' destabilizing effect confirmed in additional research on 'host-guest' triple-helical peptides incorporating various Gly-Gly-Y guest triplets. The molecular features of triple-helix protein interactions are identified using a model of a monoclonal antibody bound to collagen.

Biosynthesis experiments are performed to include guest Gly-X-Y triplets with nonpolar residues in a defined environment. Spectroscopic measurements are performed on the samples during the experiments. Results show that the X positional reference of the residues is strongly dependent on their potential for inter molecular hydrophobic interactions. The data also suggest that hydrophobic residues do not stabilize the triple helical conformation.

A study of the effects of electrostatic interactions in the triple-helix conformation of collagen-like peptides, which form ion pairs, suggests that the conformation exhibits maximum stability due to intermolecular interaction at pH values that affect ionization of both acidic and basic residues. Repulsion of charged N-terminal or C-terminal ends exerts a destabilizing effect. Removal of like-charge repulsion, single chain ion pair formation and solvent effects are few factors which have an indirect stabilizing effect on ion pairs.

The host-guest system is extended to include two adjacent tripeptide units, Gly-X-Y-Gly-X'-Y', which now encompasses all possible interactions within the collagen triple helix. Computational analysis reveal that Lys-Gly-ASp/Glu sequences are present at a frequency much greater than expected in collagen, suggesting this interaction is biologically important.

The differences between the effect of imino acids in host-guest and repeating tripeptide collagen models are discussed. The relative order in repeating tripeptides and the host-guest system are reversed in Pro-Flp-Gly.

Mutations resulting in replacement of one obligate Gly residue within the repeating [(Gly-Xaa-Yaa).sub.n] triplet pattern of the collagen type I triple helix are the major cause of osteogenesis imperfecta (OI). Phenotypes of OI involve fragile bones and range from mild to perinatal lethal. In this study, host-guest triple-helical peptides of the form acetyl-[(Gly-Pro-Hyp).sub.3]-Zaa-Pro-Hyp-[(Gly-Pro-Hyp).sub.4] -Gly-Gly-amide are used to isolate the influence of the residue replacing Gly on triple-helix stability, with Zaa = Gly, Ala, Arg, Asp, Glu, Cys, Ser, or Val. Any substitution for Zaa = Gly (melting temperature, [T.sub.m] = 45 [degrees] C) results in a dramatic destabilization of the triple helix. For Ala and Ser, [T.sub.m] decreases to [approximately equals] 10 [degrees] C, and for the Arg-, Val-, Glu-, and Asp-containing peptides,[T.sub.m] [less than] 0 [degrees]C. A Gly [direction] Cys replacement results in [[T.sub.m] [is less than] 0 [degrees]]C. under reducing conditions but shows a broad transition ([T.sub.m] [approximately equals] 19 [degrees]C) in an oxidizing environment. Addition of trimethylamine N-oxide increases [T.sub.m] by [approximately equals] 5 [degrees]C per 1 M trimethyIamine N-oxide, resulting in stable triple-helix formation for all peptides and allowing comparison of relative stabilities. The order of disruption of different Gly replacements in these peptides can be represented as Ala [less than or equal to] Ser [is less than] [CPO.sub.red] [is less than] Arg [is less than] Val [is less than] Glu [less than or equal to] Asp. The rank of destabilization of substitutions for Gly in these Gly-Pro-Hyp-rich homotrimeric peptides shows a significant correlation with the severity of natural OI mutations in the [Alpha]1 chain of type I collagen.