The design of folded miniature proteins is predicated on establishing noncovalent interactions that direct the self-assembly of discrete thermostable tertiary structures. In this work, we describe how a network of cation−π interactions present in proteins containing “WSXWS motifs” can be emulated to stabilize the core of a miniature protein. This 19-residue protein sequence recapitulates a set of interdigitated arginine and tryptophan residues that stabilize a distinctive β-strand:loop:PPII-helix topology. Validation of the compact fold determined by NMR was carried out by mutagenesis of the cation−π network and by comparison to the corresponding disulfide-bridged structure. These results support the involvement of a coordinated set of cation−π interactions that stabilize the tertiary structure.
Timothy W. Craven, Min-Kyu Cho, Nathaniel J. Traaseth, Richard Bonneau, and Kent Kirshenbaum. (2016), A Miniature Protein Stabilized by a Cation−π Interaction Network. J. Am. Chem. Soc. 138(5), 1543-1550 Link