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This brief report presents an X-ray scattering investigation of self-assembled nanotubes formed by a short peptide. X-ray scattering methods enable multiscale structural elucidation of these nanotubes in solution under the same conditions involved in the self-assembly process. In particular, the dimensions of nanotubes and the crystalline organization within their walls can be determined quantitatively. This is illustrated in the case of amyloid-beta(16-22) peptide nanotubes.

Leukotriene (LT) C4 synthase (LTC4S) catalyzes the conjugation of the fatty acid LTA4 with the tripeptide GSH to produce LTC4, the parent compound of the cysteinyl-leukotrienes, important mediators of asthma. Here we mutated Trp116 in human LTC4S, a residue proposed to play a key role in substrate binding, into an Ala or Phe. Biochemical and structural characterization of these mutants along with crystal structures of the wild type and mutated enzymes in complex with three product analogs, viz. S-hexyl-, 4- phenyl-butyl-, and 2-hydroxy-4-phenyl-butyl-glutathione, provide new insights to binding of substrates and product, identifies a new conformation of the GSH moiety at the active site, and suggests a route for product release, aided by Trp116.

We compare the aqueous self-assembly behavior within the homologous peptide series AnK, where A is alanine, K is lysine, and n = 4, 6, 8, and 10. The aqueous peptide solubility, øs (volume fraction), depends strongly on the number of hydrophobic alanine residues and decreases approximately as øs ? 10-n. Also the self-assembly structure depends on n. A4K is highly water-soluble and shows no relevant self-assembly. A6K, which has been extensively studied previously, forms hollow nanotubes in water. A8K and A 10K self-assembly is characterized here using a combination of small- and wide-angle X-ray scattering, static and dynamic light scattering, cryo transmission electron microscopy, and circular dichroism spectroscopy. They both form similar thin rodlike aggregates with lengths on the order of 100 nm and a biaxial cross-section with dimensions of 4 nm × 8 nm. We show that different sample preparation protocols result in different lengths of the A 10K rodlike aggregates. On the basis of these findings, the question of thermodynamic equilibrium of peptide self-assembly is discussed. © 2014 American Chemical Society.

We compare the aqueous self-assembly behavior within the homologous peptide series A(n)K, where A is alanine, K is lysine, and n = 4, 6, 8, and 10. The aqueous peptide solubility, phi(s) (volume fraction), depends strongly on the number of hydrophobic alanine residues and decreases approximately as phi(s) approximate to 10(-n). Also the self-assembly structure depends on n. A(4)K is highly water-soluble and shows no relevant self-assembly. A(6)K, which has been extensively studied previously, forms hollow nanotubes in water. A(8)K and A(10)K self-assembly is characterized here using a combination of small- and wide-angle X-ray scattering, static and dynamic light scattering, cryo transmission electron microscopy, and circular dichroism spectroscopy. They both form similar thin rodlike aggregates with lengths on the order of 100 nm and a biaxial cross-section with dimensions of 4 nrn x 8 nm. We show that different sample preparation protocols result in different lengths of the A(10)K rodlike aggregates. On the basis of these findings, the question of thermodynamic equilibrium of peptide self-assembly is discussed. Swedish Research Council (VR)Swedish Research Council [239-2009-6794]; Gyllenstierna Krapperup Foundation; NSFNational Science Foundation (NSF) [DMR-0520547] This work was supported by the Swedish Research Council (VR) through a Linnaeus grant for the Organizing Molecular Matter (OMM) Center of Excellence (239-2009-6794) and the Gyllenstierna Krapperup Foundation. We thank Mikael Lund and Jan Dhont for stimulating discussions. We also thank Manja Behrens for her assistance with some of the light scattering experiments and Gunnel Karlsson for her skillful performance of the cryo-TEM experiments and the discussions around them. This work benefitted from SasView software, originally developed by the DANSE project under NSF Award DMR-0520547.

Above its critical aggregation concentration the tfa salt of the peptide A6K self-assembles into micron long, hollow nanotubes with uniform diameters of 52 nm and crystalline order. Here we combine the use of SAXS with cryoTEM and cryo-electron tomography (cryoET, 3D cryoTEM) to study the formation process of the 2D crystalline A6K nanotubes. This study reveals that the formation of these tubes in fact is a crystal growth process, involving different mechanisms depending on the conditions used. Inorganic crystals have been demonstrated to form not only through ion-by-ion addition but also through non-classical mechanisms including oriented attachment. Here we show an organic crystalline material that can form through molecule-by-molecule growth as well as through oriented attachment. We discuss the mechanisms in relation to the supersaturation levels of the peptide solutions and the molecular interactions between the peptide molecules in the tubular assemblies. The proposed mechanisms are supported by semi-empirical molecular orbital calculations and time resolved dissolution experiments. © 2012 The Royal Society of Chemistry.

The self-assembly of the trifluoroacetate salt of the short peptide (ala)6-lys (A6K) in water has been investigated by cryo-transmission electron microscopy and small-angle X-ray scattering. For concentrations below ca. 12%, the peptide does not self-assemble but forms a molecularly dispersed solution. Above this critical concentration, however, A6K self-assembles into several-micrometer-long hollow nanotubes with a monodisperse cross-sectional radius of 26 nm. Because the peptides carry a positive charge, the nanotubes are charge-stabilized. Because of the very large aspect ratio, the tubes form an ordered phase that presumably is nematic. © 2009 American Chemical Society.

The DNA incorporated 1 μm size vesicular multi-lamellar aggregates were obtained. Colloidal stability of the cationic surfactant-DNA/lecithin self-assemblies obtained by “solvent shifting” method increases with lecithin content was found.