Hydrophobic Surface Burial Is the Major Stability Determinant of a Flat, Single-layer b-Sheet

• Published in: Journal of molecular biology Vol. 368; no. 1; pp. 230 - 243
• Main Authors: Yan, S, Gawlak, G, Makabe, K, Tereshko, V, Koide, A, Koide, S
• Format: Journal Article
• Language: English
• Published: 20-04-2007
• Subjects: Borrelia
• ISSN: 0022-2836
• DOI: 10.1016/j.jmb.2007.02.003

Formation of a flat b-sheet is a fundamental event in b-sheet-mediated protein self-assembly. To investigate the contributions of various factors to the stability of flat b-sheets, we performed extensive alanine-scanning mutagenesis experiments on the single-layer b-sheet segment of Borrelia outer surface protein A (OspA). This b-sheet segment consists of b-strands with highly regular geometries that can serve as a building block for self-assembly. Our Ala-scanning approach is distinct from the conventional host-guest method, in that it introduces only conservative, truncation mutations that should minimize structural perturbation. Our results showed very weak correlation with experimental b-sheet propensity scales, statistical b-sheet propensity scales, or cross-strand pairwise correlations. In contrast, our data showed strong positive correlation with the change in buried non-polar surface area. Polar interactions including prominent Glu-Lys cross-strand pairs contribute marginally to the b-sheet stability. These results were corroborated by results from additional non-Ala mutations. Taken together, these results demonstrate the dominant contribution of non-polar surface burial to flat b-sheet stability even at solvent-exposed positions. The OspA single-layer b-sheet achieves efficient hydrophobic surface burial without forming a hydrophobic core by a strategic placement of a variety of side-chains. These findings further suggest the importance of hydrophobic interactions within a b-sheet layer in peptide self-assembly.