Sugar-derived tricatenar catanionic surfactant: self-assembly and aggregation behavior in the cationic-rich side of the system

The aggregation behavior of the cationic-rich side of a sugar-based tricatenar catanionic mixture was investigated in water, and it was shown that the excess of cationic sugar-based surfactant enhanced vesicle stability as well as encapsulation properties. Moreover, when the system was diluted, the vesicular solution collapsed into a lamellar phase, whereas, when it was concentrated, no major impact on the shape and stability of the aggregates was observed. We also showed that both an increase in temperature and the addition of salt induced reversible vesicle aggregation, which appeared to be salt-specific, following the direct order of the Hofmeister series. A proper adjustment of these parameters should then enable better control of the shape, stability, and even encapsulation ability of the aggregates formed by these tricatenar cationic/anionic mixtures.

A papain-like enzyme at work: native and acyl-enzyme intermediate structures in phytochelatin synthesis

Phytochelatin synthase (PCS) is a key enzyme for heavy-metal detoxification in plants. PCS catalyzes the production of glutathione (GSH)-derived peptides (called phytochelatins or PCs) that bind heavy-metal ions before vacuolar sequestration. The enzyme can also hydrolyze GSH and GS-conjugated xenobiotics. In the cyanobacterium Nostoc, the enzyme (NsPCS) contains only the catalytic domain of the eukaryotic synthase and can act as a GSH hydrolase and weakly as a peptide ligase. The crystal structure of NsPCS in its native form solved at a 2.0-A resolution shows that NsPCS is a dimer that belongs to the papain superfamily of cysteine proteases, with a conserved catalytic machinery. Moreover, the structure of the protein solved as a complex with GSH at a 1.4-A resolution reveals a gamma-glutamyl cysteine acyl-enzyme intermediate stabilized in a cavity of the protein adjacent to a second putative GSH binding site. GSH hydrolase and PCS activities of the enzyme are discussed in the light of both structures.