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 Gβ1m 2 . Gβ1m 2 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 Gβ1m 2 was solved to 2.0 Å resolution by molecular replacement. The absence of hydrogen bond or salt bridge interactions between the designed residues in Gβ1m 2 suggests that the increased stability of Gβ1m 2 is due to increased helix propensity and more favorable helix dipole interactions.