Sequence Position and Side Chain Length Dependence of Charge Pair Interactions in Collagen Triple Helices

In this study, we examine eight ABC heterotrimers whose self-assembly is directed through electrostatic interactions. Oppositely charged pairs of amino acids, with varying side chain length, were assessed for their ability to stabilize a triple helix. Aspartate-lysine was found to result in the most thermally stable helix followed by lysine-glutamate, ornithine-aspartate, and finally ornithine-glutamate. When the sequence position of these charged amino acids was reversed from what is normally observed in nature, triple helix stability and compositional purity were significantly reduced. We examine the effect of salt on triple helix stability and observe that increased salt concentration reduces the thermal stability of heterotrimers by an average of 5 C, but does not disrupt helix assembly. It was also found that some highly positively charged homotrimers can be stabilized in the presence of phosphate anions.