Molecular Dynamics of DNA Translocation by FtsK

The bacterial FtsK motor harvests energy from ATP to translocate double-stranded DNA during cell division. Here, we probe the molecular mechanisms underlying coordinated DNA translocation in FtsK by performing long timescale simulations of its hexameric assembly and individual subunits. From these simulations we predict signaling pathways that connect the ATPase active site to DNA-gripping residues, which allows the motor to coordinate its translocation activity with its ATPase activity. Additionally, we utilize well-tempered metadynamics simulations to compute free-energy landscapes that elucidate the extended-to-compact transition involved in force generation. We show that nucleotide binding promotes a compact conformation of a motor subunit, whereas the apo subunit is flexible. Together, our results support a mechanism whereby each ATP-bound subunit of the motor conforms to the helical pitch of DNA, and ATP hydrolysis/product release causes a subunit to lose grip of DNA. By ordinally engaging and disengaging with DNA, the FtsK motor unidirectionally translocates DNA.

Release Rates of Short-lived Fission Gases from Modern Spherical Fuel Elements with TRISO-coated Particles

Measurement and prediction of fission product release is important in design, licensing and operation of HTRs. Latest development status is near zero particle manufacturing defects and in-pile failures combined with very low matrix contamination levels. In-pile Release over Birth rate measurements will be described and evaluated. Quantitative predictive analyses of short-lived gas release will be provided for MTR irradiation testing with a focus on the most recent experiment with Chinese fuel from HTR-PM production. For irradiation tests with no single particle failure, models describing particle kernel release are not applicable; instead modeling of matrix contamination release is essential. Good agreement between post calculations and in-line R/B measurements has been achieved.

Opening the side exit pores of ClpP by lowering the pH of proteolytic chamber coupled with substrate hydrolysis

The ClpP serine peptidase is a tetradecameric degradation machine involved in many physiological processes. It becomes a competent ATP-dependent protease with Clp-ATPases. Small chemical compounds, acyldepsipeptides (ADEPs), are known to cause dysregulation and activation of ClpP without ATPases, and have potential as novel antibiotics. Previously, structural studies of ClpP from various species revealed the structural details, conformational changes, and activation mechanism. Although product release by the side exit pores has been proposed, the detailed driving force for product release remains elusive. Here, we report crystal structures of ClpP from Bacillus subtilis (BsClpP) in unforeseen ADEP-bound states. Cryo-electron microscopy structures revealed various conformational states at different pH conditions. To understand the conformational change for product release, we investigated the relationship between substrate hydrolysis and the pH lowering process. Our data, together with previous findings, provide insight into the molecular mechanism of product release by ClpP self-compartmentalizing protease.