Aromatic cluster mutations produce focal modulations of [beta]-sheet structure

• Published in: Protein science 2015-05, Vol.24 (5), p.841
• Main Authors: Biancalana, Matthew, Makabe, Koki, Yan, Shude, Koide, Shohei
• Format: Article
• Language: English
• Subjects: Amino acids; Mutation; Proteins
• ISSN: 0961-8368; 1469-896X
• DOI: 10.1002/pro.2657

Site-directed mutagenesis is a powerful tool for altering the structure and function of proteins in a focused manner. Here, we examined how a model [beta]-sheet protein could be tuned by mutation of numerous surface-exposed residues to aromatic amino acids. We designed these aromatic side chain "clusters" at highly solvent-exposed positions in the flat, single-layer [beta]-sheet of Borrelia outer surface protein A (OspA). This unusual [beta]-sheet scaffold allows us to interrogate the effects of these mutations in the context of well-defined structure but in the absence of the strong scaffolding effects of globular protein architecture. We anticipated that the introduction of a cluster of aromatic amino acid residues on the [beta]-sheet surface would result in large conformational changes and/or stabilization and thereby provide new means of controlling the properties of [beta]-sheets. Surprisingly, X-ray crystal structures revealed that the introduction of aromatic clusters produced only subtle conformational changes in the OspA [beta]-sheet. Additionally, despite burying a large degree of hydrophobic surface area, the aromatic cluster mutants were slightly less stable than the wild-type scaffold. These results thereby demonstrate that the introduction of aromatic cluster mutations can serve as a means for subtly modulating [beta]-sheet conformation in protein design. PDB Code(s): 2PI3; 2OY5; 3AUM