Structure of a protein G helix variant suggests the importance of helix propensity and helix dipole interactions in protein design

Six helix surface positions of protein G (G beta 1) were redesigned using a computational protein design algorithm, resulting in the five fold mutant G beta 1m2. G beta 1m2 is well folded with a circular dichroism spectrum nearly identical to that of G beta 1, and a melting temperature of 91 degrees C, similar to 6 degrees C higher than that of G beta 1. The crystal structure of G beta 1m2 was solved to 2.0 Angstrom resolution by molecular replacement. The absence of hydrogen bond or salt bridge interactions between the designed residues in G beta 1m2 suggests that the increased stability of G beta 1m2 is due to increased helix propensity and more favorable helix dipole interactions.