Large conformational changes in MutS during DNA scanning, mismatch recognition and repair signalling.

MutS protein recognizes mispaired bases in DNA and targets them for mismatch repair. Little is known about the transient conformations of MutS as it signals initiation of repair. We have used single-molecule fluorescence resonance energy transfer (FRET) measurements to report the conformational dynamics of MutS during this process. We find that the DNA-binding domains of MutS dynamically interconvert among multiple conformations when the protein is free and while it scans homoduplex DNA. Mismatch recognition restricts MutS conformation to a single state. Steady-state measurements in the presence of nucleotides suggest that both ATP and ADP must be bound to MutS during its conversion to a sliding clamp form that signals repair. The transition from mismatch recognition to the sliding clamp occurs via two sequential conformational changes. These intermediate conformations of the MutS:DNA complex persist for seconds, providing ample opportunity for interaction with downstream proteins required for repair.

DnaN clamp zones provide a platform for spatiotemporal coupling of mismatch detection to DNA replication.

Mismatch repair (MMR) increases the fidelity of DNA replication by identifying and correcting replication errors. Processivity clamps are vital components of DNA replication and MMR, yet the mechanism and extent to which they participate in MMR remains unclear. We investigated the role of the Bacillus subtilis processivity clamp DnaN, and found that it serves as a platform for mismatch detection and coupling of repair to DNA replication. By visualizing functional MutS fluorescent fusions in vivo, we find that MutS forms foci independent of mismatch detection at sites of replication (i.e. the replisome). These MutS foci are directed to the replisome by DnaN clamp zones that aid mismatch detection by targeting the search to nascent DNA. Following mismatch detection, MutS disengages from the replisome, facilitating repair. We tested the functional importance of DnaN-mediated mismatch detection for MMR, and found that it accounts for 90% of repair. This high dependence on DnaN can be bypassed by increasing MutS concentration within the cell, indicating a secondary mode of detection in vivo whereby MutS directly finds mismatches without associating with the replisome. Overall, our results provide new insight into the mechanism by which DnaN couples mismatch recognition to DNA replication in living cells.

Antioxidant and antiplatlet aggregation properties of bark extracts of Garcinia pedunculata and Garcinia cowa.

The bark extracts of Garcinia pedunculata and Garcinia cowa, which are abundant in the Northeastern regions of India, were screened for their antioxidant and in vitro antiplatelet aggregating activities. By ß-carotene linoleate model for antioxidant assay, acetone extract of G. pedunculata and hexane extracts of G. cowa exhibited higher antioxidant activity (86.47 and 66.94 % respectively, at 25 ppm) than other extracts. Similar pattern was observed for superoxide radical scavenging method for antioxidant assay. The ethyl acetate extract of G. pedunculata and hexane extract of G. cowa exhibited higher antiplatelet aggregation capacity towards ADP induced platelet aggregation (IC50 0.16 and 0.43 ug, respectively) than other extracts.

Lightweight carbon-red mud hybrid foam toward fire-resistant and efficient shield against electromagnetic interference.

Lightweight, porous, high-performance electromagnetic interference (EMI) shielding and fire-resistant materials are highly demanded in aerospace and defense applications. Due to the lightweight, open porosity and high surface area, carbon foam has been considered as one of the most promising candidates for EMI shielding applications. In the present investigation, we demonstrate the development of novel carbon-red mud hybrid foams with excellent EMI shielding effectiveness (SE). The carbon-red mud hybrid foams are prepared using phenolic resin as a carbon source and red mud (industrial waste) as filler. We observed that the inclusion of red mud in carbon-red mud hybrid foams significantly enhances their dielectric, magnetic, EMI shielding and thermal properties. The EMI shielding results show that absorption is the main contributor to the total EMI SE. The maximum total EMI shielding effectiveness is achieved to be 51.4 dB in the frequency range of 8.2-12.4 GHz for carbon-red mud hybrid foam having 20 wt. % of red mud. The CF-RM20 also showed excellent fire resistance and high thermal stability at elevated temperatures.

Slow conformational changes in MutS and DNA direct ordered transitions between mismatch search, recognition and signaling of DNA repair.

MutS functions in mismatch repair (MMR) to scan DNA for errors, identify a target site and trigger subsequent events in the pathway leading to error removal and DNA re-synthesis. These actions, enabled by the ATPase activity of MutS, are now beginning to be analyzed from the perspective of the protein itself. This study provides the first ensemble transient kinetic data on MutS conformational dynamics as it works with DNA and ATP in MMR. Using a combination of fluorescence probes (on Thermus aquaticus MutS and DNA) and signals (intensity, anisotropy and resonance energy transfer), we have monitored the timing of key conformational changes in MutS that are coupled to mismatch binding and recognition, ATP binding and hydrolysis, as well as sliding clamp formation and signaling of repair. Significant findings include (a) a slow step that follows weak initial interaction between MutS and DNA, in which concerted conformational changes in both macromolecules control mismatch recognition, and (b) rapid, binary switching of MutS conformations that is concerted with ATP binding and hydrolysis and (c) is stalled after mismatch recognition to control formation of the ATP-bound MutS sliding clamp. These rate-limiting pre- and post-mismatch recognition events outline the mechanism of action of MutS on DNA during initiation of MMR.