Destabilization of osteogenesis imperfecta collagen-like model peptides correlates with the identity of the residue replacing glycine

Mutations resulting in replacement of one obligate Gly residue within the repeating (Gly-Xaa-Yaa)(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)(3)-Zaa-Pro-Hyp-(Gly-Pro-hyp)(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-m = 45 degrees C) results in a dramatic destabilization of the triple helix. For Ala and ser, T-m decreases to approximate to 10 degrees C, and for the Arg-, Val-, Glu-, and Asp-containing peptides, T-m < 0 degrees C. A Gly --> Cys replacement results in T-m < 0 degrees C under reducing conditions but shows a broad transition (T-m approximate to 19 degrees C) in an oxidizing environment. Addition of trimethylamine N-oxide increases T-m by approximate to 5 degrees C per 1 M trimethylamine 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 < CPOred < Arg < Val < Glu less than or equal to Asp. The rank of destabilization of substitutions for Gly in these Gly-ProHyp-rich homotrimeric peptides shows a significant correlation with the severity of natural OI mutations in the alpha 1 chain of type I collagen.