Effects of Increased Loop Flexibility on the Structure and Stability of a De Novo Designed Helical Protein.

MB-1 is a de novo protein designed to incorporate amino acids required for dairy cow nutrition while folding into a four-helix-bundle. Analysis shows that, as per design, MB-1 is a largely helical protein but appears to be dimeric and shows less stability than expected. Recent evidence indicates that the loop regions in MB-1 may have been under-designed. The variant, MB-16, described here attempts to correct potentially detrimental effects on turn formation by introducing a flexible, five-glycine residues sequence as the second loop.