No abstract

Giant rod–coil amphiphilic block copolymers were prepared by metallocene‐catalyzed polymerization. The hydrophilic coiled block consists of polymethacrylic acid and the rod component of a hydrophobic cylindrical brush polymer. The high solubility of the stiff block results in the micelles being formed with the stiff block forming the solubilizing corona.

A high-molar-mass cylindrical brush polymer with a main chain degree of polymerization of Pw = 1047 is synthesized by free-radical polymerization of a poly-2-isopropyloxazoline macromonomer with Pn = 28. The polymerization is conducted above the lower phase transition temperature of the macromonomer, i.e., in the phase-separated regime, which provides a sufficiently concentrated macromonomer phase mandatory to obtain high-molar-mass cylindrical brushes. Upon heating to the phase transition temperature, the hydrodynamic radius is observed to shrink from 34 to 27 nm. Further increase in temperature resulted in aggregated chains which were observed to coexist with single chains until eventually only aggregates of μm size were detectable.

Cylindrical brush polymers with poly-L-lysine side chains were prepared by grafting lysine NCA from a macroinitiator via living ring-opening polymerization. The main chain degree of polymerization of the methacrylate main chain was P w = 870, the side chains consisted of 25 and 55 lysine repeat units, respectively. Upon deprotection, the cylindrical brush polymers in 0.005 M NaBr exhibited an almost rodlike conformation with a Kuhn statistical segment length of several hundred nanometers. Cryo-TEM as well as AFM in aqueous solution clearly demonstrated pronounced undulations along the main chain at low ionic strength which could not be detected at higher salt concentrations. With increasing concentration of NaClO 4 the PLL side chains underwent a coil-to-helix transition as revealed by CD measurements. The effect of the side chain coil-to-helix transition on the main chain stiffness could not be followed by light scattering due to intramolecular attraction ("folding") of the cylindrical brushes at high salt concentration, which is somewhat more pronounced for the helical as compared to the coiled PLL side chain conformation. Comparison with linear PLL revealed the coil-to-helix transition to be hardly affected by the high grafting density of the PLL side chains in the cylindrical brush structures.

Silicateins are crucial enzymes that are involved in formation of the inorganic biosilica scaffold of the spicular skeleton of siliceous sponges. We show that silicatein acquires its structure-guiding and enzymatically active state by processing of silicatein from pro-silicatein to the mature enzyme. A recombinant propeptide (PROP) of silicatein from the siliceous demosponge Suberites domuncula was prepared, and antibodies were raised against the peptide. In sponge tissue, these antibodies reacted with both surface structures and the central region of the spicules. Using phage display expression, spicule-binding 12-mer peptides were identified that are rich in histidine residues. In the predicted tertiary structure of PROP, these histidine residues are only present in the a-helical region. The recombinant PROP was found to inhibit self-assembly of silicatein molecules. By light scattering, it was shown that, in the presence of 4 M urea, the recombinant silicatein is obtained in the mono/oligomeric form with a hydrodynamic radius of 4 nm, while lower urea concentrations promote self-aggregation and assembly of the protein. Finally, it is shown that the enzymatic activity of silicatein is abolished by PROP in silicatein samples that predominantly contain mono-or oligomeric silicatein particles, but the enzyme is not affected if present in the filamentous aggregated form. It is concluded that the functions of silicatein, acting as a structural template for its biosilica product and as an enzyme, are modulated and controlled by its propeptide. Structured digital abstractalpha-silicatein and alpha-silicatein bind by transmission electron microscopy (View interaction)[Structured digital abstract was added on 27 March 2013 after original online publication]