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 (Gβ1) were redesigned using a computational protein design algorithm, resulting in the five fold mutant Gβ1m2. Gβ1m2 is well folded with a circular dichroism spectrum nearly identical to that of Gβ1, and a melting temperature of 91 °C, ∼6 °C higher than that of Gβ1. The crystal structure of Gβ1m2 was solved to 2.0 Å resolution by molecular replacement. The absence of hydrogen bond or salt bridge interactions between the designed residues in Gβ1m2 suggests that the increased stability of Gβ1m2 is due to increased helix propensity and more favorable helix dipole interactions.