Molecular mechanism for target recognition, dimerization, and activation of Pyrococcus furiosus Argonaute.

The Argonaute nuclease from the thermophilic archaeon Pyrococcus furiosus (PfAgo) contributes to host defense and represents a promising biotechnology tool. Here, we report the structure of a PfAgo-guide DNA-target DNA ternary complex at the cleavage-compatible state. The ternary complex is predominantly dimerized, and the dimerization is solely mediated by PfAgo at PIWI-MID, PIWI-PIWI, and PAZ-N interfaces. Additionally, PfAgo accommodates a short 14-bp guide-target DNA duplex with a wedge-type N domain and specifically recognizes 5'-phosphorylated guide DNA. In contrast, the PfAgo-guide DNA binary complex is monomeric, and the engagement of target DNA with 14-bp complementarity induces sufficient dimerization and activation of PfAgo, accompanied by movement of PAZ and N domains. A closely related Argonaute from Thermococcus thioreducens adopts a similar dimerization configuration with an additional zinc finger formed at the dimerization interface. Dimerization of both Argonautes stabilizes the catalytic loops, highlighting the important role of Argonaute dimerization in the activation and target cleavage.

[Effects of cadmium stress on xanthine oxidase and antioxidant enzyme activities in Boleophthalmus pectinirostris liver].

This paper approached the feasibility of using the xanthine oxidase (XOD), superoxide dismutase (SOD) and catalase (CAT) activities and malonyldialdehyde (MDA) content in Boleophthalmus pectinirostris liver as the indicators of Cd2+ toxic effects on this marine fish. Three concentrations of cadmium chloride (0.05, 0.5 and 5 mg Cd2+ x L(-1)) were enacted. The results showed that in treatment 0.05 mg Cd2+ x L(-1), the XOD and SOD activities in B. pectinirostris liver increased with time and reached the maximum on the 10th day, while in treatments 0.5 and 5 mg Cd2+ x L(-1), they increased significantly or extremely significantly, compared with the control. The CAT activity in treatments 0.05 and 5 mg Cd2+ x L(-1) decreased significantly within 12 hours, but recovered then in treatment 0.05 mg Cd2+ x L(-1). After moved into clean seawater for 5 days, the CAT activity increased extremely significantly in treatments 0. 5 and 5 mg Cd2+ x L(-1), but reversed in treatment 0.05 mg Cd2+ x L(-1). As a product of antioxidation and oxidation, the content of MDA in treatments 0.5 and 5 mg Cd2+ x L(-1) decreased extremely significantly after recovered for 5 days. It was suggested that the XOD and SOD activities in B. pectinirostris liver could be used as a biomarker of Cd2+ pollution, while the CAT activity and MDA content in this marine fish liver were not sensitive to Cd2+ stress.