Xu Q, Biancalana M, Grant JC, Chiu H, Jaroszewski L, Knuth MW, Lesley SA, Godzik A, Elsliger M, Deacon AM, Wilson IA. Structures of single-layer β-sheet proteins evolved from β-hairpin repeats.
Protein Sci 2019;
28:1676-1689. [PMID:
31306512 PMCID:
PMC6699103 DOI:
10.1002/pro.3683]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 07/08/2019] [Accepted: 07/08/2019] [Indexed: 11/09/2022]
Abstract
Free-standing single-layer β-sheets are extremely rare in naturally occurring proteins, even though β-sheet motifs are ubiquitous. Here we report the crystal structures of three homologous, single-layer, anti-parallel β-sheet proteins, comprised of three or four twisted β-hairpin repeats. The structures reveal that, in addition to the hydrogen bond network characteristic of β-sheets, additional hydrophobic interactions mediated by small clusters of residues adjacent to the turns likely play a significant role in the structural stability and compensate for the lack of a compact hydrophobic core. These structures enabled identification of a family of secreted proteins that are broadly distributed in bacteria from the human gut microbiome and are putatively involved in the metabolism of complex carbohydrates. A conserved surface patch, rich in solvent-exposed tyrosine residues, was identified on the concave surface of the β-sheet. These new modular single-layer β-sheet proteins may serve as a new model system for studying folding and design of β-rich proteins.
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