Two-dimensional order in β-sheet peptide monolayers

Amphiphilic peptides comprising alternating hydrophilic and hydrophobic amino acid residues were designed to form super-secondary structures composed of self-assembled β-strands as monolayers at the air−water interface. Insights provided by in situ grazing-incidence X-ray diffraction (GIXD), surface pressure vs area isotherms, and Fourier transform infrared spectroscopy allow structural characterization of the assembled nanostructures and rational correlation with the peptide sequence. Peptides seven to seventeen amino acids in length were found to form crystalline arrays with coherence lengths in the range of 100 to 1000 Å. Two-dimensional registry of the self-assembled peptides was induced by placement of proline residues at the peptide termini. The films were found to intercalate ordered arrays of ions between juxtaposed β-sheet ribbons to generate peptide−ion composite phases

Efficient incorporation of unsaturated methionine analogues into proteins in vivo

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Expanding the scope of protein biosynthesis via introduction of a mutant methionyl-tRNA synthetase

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Expanding the scope of protein biosynthesis by altering the methionyl-tRNA synthetase activity of a bacterial expression host

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Parallel β-sheet assemblies at interfaces

Polypeptide assemblies may exhibit various topologies[1-9] that are of interest for nanometer-scale surface patterning and its potential applications. The success in designing such ordered molecular architectures entails control over peptide conformations and intermolecular interactions. At the air-water interface peptides composed of alternating hydrophilic and hydrophobic amino acids tend to adopt β-sheet structures[10] yet the repetitive nature of these peptides also promotes nonspecific intermolecular aggregation. Recently, in several systems of de novo designed b-sheet peptides two-dimensional order has been demonstrated by grazing incidence X-ray diffraction[8, 9] and by scanning probe microscopy;[11] the extent of molecular registry has been associated with peptide composition and molecular chain length. Here we aim at formation of parallel β-sheet ordered assemblies at interfaces by using strands programmed to adopt distinct intermolecular electrostatic interactions

Assembly of triple-stranded β-sheet peptides at interfaces

A 30-residue peptide, BS30, which incorporates two proline residues to induce reverse turns, was designed to form a triple-stranded β-sheet monolayer at the air−water interface. To discern the structural role of proline, a second peptide, BS30G, identical to BS30 but with glycine residues replacing proline, was prepared and examined in parallel fashion. Surface pressure−molecular area isotherms indicated a limiting area per molecule (ca. 460 Å^2) for BS30 that corresponds well to that estimated from the known dimensions of crystalline β-sheet monolayers (492 Å^2). Comparable measurements on BS30G yielded a smaller molecular area (380 Å^2). Grazing incidence X-ray diffraction measurements performed on the BS30 monolayer at nominal area per molecule of 500 Å^2, exhibited two Bragg peaks corresponding to 4.79 and 34.9 Å spacings, consistent with formation of triple-stranded β-sheet structures that assemble into two-dimensional crystallites at the air−water interface. Visualized by Brewster angle microscopy, BS30 monolayers displayed uniform, solidlike domains, whereas BS30G appeared to be disordered