The properties
of synthetic peptides, including potency, stability,
and bioavailability, are strongly influenced by modification of the
peptide chain termini. Unfortunately, generally applicable methods
for selective and mild C-terminal peptide functionalization are lacking.
In this work, we explored the peptide amidase from Stenotrophomonas
maltophilia as a versatile catalyst for diverse carboxy-terminal
peptide modification reactions. Because the scope of application of
the enzyme is hampered by its mediocre stability, we used computational
protein engineering supported by energy calculations and molecular
dynamics simulations to discover a number of stabilizing mutations.
Twelve mutations were combined to yield a highly thermostable (Δ
T
m = 23 °C) and solvent-compatible
enzyme. Protein crystallography and molecular dynamics simulations
revealed the biophysical effects of mutations contributing to the
enhanced robustness. The resulting enzyme catalyzed the
selective C-terminal modification of synthetic peptides with small
nucleophiles such as ammonia, methylamine, and hydroxylamine in various
organic (co)solvents. The use of a nonaqueous environment allowed
modification of peptide free acids with >85% product yield under
thermodynamic
control. On the basis of the crystal structure, further mutagenesis
gave a biocatalyst that favors introduction of larger functional groups.
Thus, the use of computational and rational protein design provided
a tool for diverse enzymatic peptide modification.
Click to switch: A novel family of azobenzenes containing residues needed for aqueous Staudinger–Bertozzi ligation to azides was designed (see scheme). The resulting photochromes show stable and reversible switching behavior in water, with a photostationary state (PSS) of up to 95:5 cis/trans. Applications in model systems include the modification of azide‐bearing surfaces and proteins.
A mild and convenient oxidative transformation of secondary alcohols to 1,5‐disubstituted tetrazoles is uncovered by employing trimethylsilyl azide (TMSN3) as a nitrogen source in the presence of a catalytic amount of copper(II) perchlorate hexahydrate [Cu(ClO4)2.6 H2O] (5 mol%) and 2,3‐dichloro‐5,6‐dicyano‐para‐benzoquinone (DDQ) (1.2 equiv.) as an oxidant. This reaction is performed under ambient conditions and proceeds through CC bond cleavage.
The solid-phase synthesis and full chemical characterization of the medium-length (14-amino acid residues) peptaibol with antibiotic properties of tylopeptin B, originally extracted from the fruiting body of the mushroom Tylopilus neofelleus, are described. These data are accompanied by the results on the solution-phase synthesis via the segment condensation approach of a selected, side-chain protected, analog. A solution conformational analysis, performed by the combined use of FTIR absorption, circular dichroism, and 2D-NMR (the latter technique coupled to molecular dynamics calculations), favors the conclusion that the 3D-structure of tylopeptin B is largely helical with a preference for the a-or the 3 10 -helix type depending upon the nature of the solvent. Helix topology and (partial) amphiphilic character are responsible for the observed membrane-modifying properties of this peptaibiotic.
The use of an overcrowded alkene photoswitch to control a model β-hairpin peptide is described. The light-induced, large conformational change has major influence on the secondary structure and the aggregation of the peptide, permitting the triggered formation of amyloid-like fibrils.
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