Polypeptide nanoribbon hydrogels assembled through multiple supramolecular interactions.

We investigated the formation of nanoribbon hydrogels in a mixed system of zinc ions, bis(ligand)s, and triblock peptide copolymers. Using a combination of experimental techniques: dynamic light scattering, cryo-transmission electron microscopy, small-angle X-ray scattering and circular dichroism, we arrived at a model for the formation of nanoribbon hydrogels in which well-defined nanoribbons are formed out of multiple supramolecular interactions: (1) metal coordination that yields supramolecular polyelectrolytes; (2) electrostatic complexation between the supramolecular polyelectrolytes and the oppositely charged blocks of the peptide copolymers; (3) hydrogen bond and (4) hydrophobic interactions that support the secondary and ternary structure of the ribbons; (5) van der Waals interactions that enable bundling of the ribbons.

Substrate-induced production and secretion of cellulases by Clostridium acetobutylicum.

Clostridium acetobutylicum ATCC 824 is a solventogenic bacterium that grows heterotrophically on a variety of carbohydrates, including glucose, cellobiose, xylose, and lichenan, a linear polymer of beta-1,3- and beta-1,4-linked beta-D-glucose units. C. acetobutylicum does not degrade cellulose, although its genome sequence contains several cellulase-encoding genes and a complete cellulosome cluster of cellulosome genes.

Production by Clostridium acetobutylicum ATCC 824 of CelG, a cellulosomal glycoside hydrolase belonging to family 9.

The genome sequence of Clostridium acetobutylicum ATCC 824, a noncellulolytic solvent-producing strain, predicts the production of various proteins with domains typical for cellulosomal subunits. Most of the genes coding for these proteins are grouped in a cluster similar to that found in cellulolytic clostridial species, such as Clostridium cellulovorans. CAC0916, one of the open reading frames present in the putative cellulosome gene cluster, codes for CelG, a putative endoglucanase belonging to family 9, and it was cloned and overexpressed in Escherichia coli.