Short sequences of non-proline residues can adopt the polyproline II helical conformation

The left-handed polyproline II (P-II) helix is a structure that has been given a great deal of attention lately because of its role in a wide variety of physiologically important processes and potential significance in protein unfolded states. Recent work by several authors has shown that residues besides proline can adopt this structure. A scale of relative P-II-helix-forming propensities has been generated but only for single guest residues in a proline-based host system. Here, we present multiple guest residues in a proline-based host system. Using circular dichroism spectroscopy, we have shown that not only single residues, but also short sequences of non-proline residues can adopt the P-II conformation.