Hydrophobic surface burial is the major stability determinant of a flat, single-layer beta-sheet.
Formation of a flat beta-sheet is a fundamental event in beta-sheet-mediated protein self-assembly. To investigate the contributions of various factors to the stability of flat beta-sheets, we performed extensive alanine-scanning mutagenesis experiments on the single-layer beta-sheet segment of Borrelia outer surface protein A (OspA). This beta-sheet segment consists of beta-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 beta-sheet propensity scales, statistical beta-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 beta-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 beta-sheet stability even at solvent-exposed positions. The OspA single-layer beta-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 beta-sheet layer in peptide self-assembly.
Yan
Shude
S
Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
Gawlak
Grzegorz
G
Makabe
Koki
K
Tereshko
Valentina
V
Koide
Akiko
A
Koide
Shohei
S
D000409:Alanine / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000954:Antigens, Surface / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001428:Bacterial Vaccines / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D025065:Borrelia burgdorferi; D018360:Crystallography, X-Ray; D018698:Glutamic Acid / Q000235:genetics; D057927:Hydrophobic and Hydrophilic Interactions; D008074:Lipoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008239:Lysine / Q000235:genetics; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary
D000954:Antigens, Surface; D001425:Bacterial Outer Membrane Proteins; D001428:Bacterial Vaccines; D008074:Lipoproteins; D050505:Mutant Proteins; C072045:OspA protein; D018698:Glutamic Acid; D008239:Lysine; D000409:Alanine