Spectroscopic study of environment-dependent changes in the conformation of the isolated carboxy-terminal telopeptide of type I collagen.

The C-terminal telopeptide of the alpha 1 chain of type I collagen from bovine skin was isolated from a bacterial collagenase digest. Two forms of the telopeptide were obtained, one with two and the other with three residues of tyrosine. In both of these, the single lysyl residue had been oxidized to alpha-aminoadipic delta-semialdehyde. Circular dichroism spectra of the telopeptide in aqueous solution at neutral pH were interpreted as indicating the presence of little regular secondary structure. However, sodium dodecyl sulfate at a concentration of 40 mM induced some alpha helix, as predicted from the sequence, and trifluoroethanol also induced secondary structure, probably a mixture of alpha helix and beta sheet. A major feature of the circular dichroism spectra of the telopeptide in sodium dodecyl sulfate, in denaturing agents, and in sodium phosphate buffer at low temperature was a positive band at 227 nm due to tyrosine side-chain chromophores. The disappearance of this band on heating and at high pH was ascribed to the adoption by the telopeptide of a specific tertiary structure. Poly(ethylene glycol) 1000 used as a perturbant in UV difference spectroscopy caused conformational changes resulting in decreased accessibility of tyrosine side chains and transfer of these to a less polar environment. A structural model in which the four aromatic side chains of the telopeptide are arranged in two pairs with the rings antiparallel is proposed to account for these results.