STABILIZATION OF THE COLLAGEN TRIPLE HELIX WITH A RUTHENIUM(II) ANCHOR

Abstract

Two collagen analogues based on a (Pro-Hyp-Gly)7 core were given metal-binding ability by linking histidine to either the N- or C- termini using a six-carbon spacer. Circular dichroism studies confirmed that the isomers, dubbed HPOG and POGH, form triple-helices which cooperatively unwind at Tm = 34.8 and 35.6 °C, respectively. Three strands of the HPOG peptide were bound to a ruthenium ion, by heating in the presence of tris(pyrazol-1-yl)borato ruthenium(II) (Tp-Ru). The strands of the N-Anchored complex unwind at a temperature about 10 °C higher, but do so over a broader temperature span. Thus, immobilization of collagen on a metal ion hub appears to increase helix stability while decreasing cooperativity of folding/unfolding. DFT calculations suggest that the loss of cooperativity arises from the disruption of interstrand hydrogen bonding. Other spacer groups, or other metal ions, may be necessary to promote optimal approach of strands to each other.