Biology subjects

Jardine, P. J.

Publications and source records attributed to Jardine, P. J..

6 recordsLinked to original sources

bioRxiv2025

Regulation of Ordinal DNA Translocation Cycle in Bacteriophage {varphi}29 through Trans-Subunit Interactions

Certain viruses such as tailed bacteriophages and herpes simplex virus package double-stranded DNA into empty procapsids via powerful, ring-shaped molecular motors. High resolution structures and force measurements on the DNA packaging motor of bacteriophage {Phi}29 revealed that its five ATPase subunits coordinate ATP hydrolysis with each other to maintain the proper cyclic sequence of DNA translocation steps about the ring. Here, we explore how the {Phi}29 motor regulates translocation by timing key events, namely ATP binding/hydrolysis and DNA gripping, through trans-subunit interactions. We used subunit dimers bound to DNA as our model system, a minimal system that still captures the conformation and trans-subunit interactions of the full pentametric motor complex. Molecular dynamics simulations of all-ATP and mixed ATP-ADP dimers revealed that the nucleotide occupancy of one subunit strongly affects the ability to hydrolyze ATP in the adjacent subunit by altering the free energy landscape of its catalytic glutamate approaching the gamma phosphate of ATP. Specifically, one ATP-bound subunit donates residues in trans that sterically block the neighboring subunits catalytic glutamate. This steric hindrance is resolved when the first subunit hydrolyzes ATP and is ADP-bound. This obstructive mechanism is supported by functional mutagenesis and appears to be conserved across several {Phi}29 relatives. Mutual information analysis of our simulations revealed intersubunit signaling pathways, via the trans-acting obstructive residues, that allow for sensing and communication between the binding pockets of adjacent subunits. This work shows that the sequential order of DNA translocation events amongst subunits is preserved through novel trans-subunit interactions and pathways.

molecular biology↗

bioRxiv2023

Role of DNA-DNA sliding friction and non-equilibrium dynamics in viral genome ejection and packaging

Many viruses eject their DNA via a nanochannel in the viral shell, driven by internal forces arising from the high-density genome packing. The speed of DNA exit is controlled by friction forces that limit the molecular mobility, but the nature of this friction is unknown. We introduce a method to probe the mobility of the tightly confined DNA by measuring DNA exit from phage phi29 capsids with optical tweezers. We measure extremely low initial exit velocity, a regime of exponentially increasing velocity, stochastic pausing that dominates the kinetics, and large dynamic heterogeneity. Measurements with variable applied force provide evidence that the initial velocity is controlled by DNA-DNA sliding friction, consistent with a Frenkel-Kontorova model for nanoscale friction. We confirm several aspects of the ejection dynamics predicted by theoretical models. Features of the pausing suggest it is connected to the phenomenon of "clogging" in soft-matter systems. Our results provide evidence that DNA-DNA friction and clogging control the DNA exit dynamics, but that this friction does not significantly affect DNA packaging.

biophysics↗

bioRxiv2022

Structural basis of DNA packaging by a ring-type ATPase from an archetypal viral system

Many essential cellular processes rely on substrate rotation or translocation by a multi-subunit, ring-type NTPase. A large number of double-stranded DNA viruses, including tailed bacteriophages and herpes viruses, use a homomeric ring ATPase to processively translocate viral genomic DNA into procapsids during assembly. Our current understanding of viral DNA packaging comes from three archetypal bacteriophage systems: cos, pac and phi29. Detailed mechanistic understanding exists for pac and phi29, but not for cos. Here we reconstituted in vitro a cos packaging system based on bacteriophage HK97 and provided a detailed biochemical and structural description. We used a photobleaching-based, single-molecule assay to determine the stoichiometry of the DNA-translocating ATPase large terminase. Crystal structures of the large terminase and DNA-recruiting small terminase, a first for both this phage and a cos system, reveal unexpected mechanistic similarities between cos and pac systems. At the same time, mutational and biochemical analyses indicate a new regulatory mechanism for ATPase multimerization and coordination in the HK97 system. This work therefore establishes a framework for studying the evolutionary relationships between ATP-dependent DNA translocation machineries in double-stranded DNA viruses.

biochemistry↗

bioRxiv2020

The NMR structure of a vestigial nuclease provides insight into the evolution of functional transitions in viral dsDNA packaging motors

SummaryDouble-stranded DNA viruses use ATP-powered molecular motors to package their genomes. To do so, these motors must efficiently transition between initiation, translocation, and termination modes. Here, we report structural and biophysical analyses of the C-terminal domain of the bacteriophage phi29 ATPase (CTD) that suggest a structural basis for these functional transitions. Sedimentation experiments show that the inter-domain linker in the full-length protein promotes dimerization and thus may play a role in assembly of the functional motor. The NMR solution structure of the CTD indicates it is a vestigial nuclease domain that likely evolved from conserved nuclease domains in phage terminases. Despite the loss of nuclease activity, fluorescence binding assays confirm the CTD retains its DNA binding capabilities and fitting the CTD into cryoEM density of the phi29 motor shows that the CTD directly binds DNA. However, the interacting residues differ from those identified by NMR titration in solution, suggesting that packaging motors undergo conformational changes to transition between initiation, translocation, and termination.Competing Interest StatementThe authors have declared no competing interest.View Full Text

biophysics↗

bioRxiv2020

A viral genome packaging motor transitions between cyclic and helical symmetry to translocate dsDNA

Molecular segregation and biopolymer manipulation require the action of molecular motors to do work by applying directional forces to macromolecules. The additional strand conserved E (ASCE) ring motors are an ancient family of molecular motors responsible for diverse tasks ranging from biological polymer manipulation (e.g. protein degradation and chromosome segregation) to establishing and maintaining proton gradients across mitochondrial membranes. Viruses also utilize ASCE segregation motors to package their genomes into their protein capsids and serve as accessible experimental systems due to their relative simplicity. We show by CryoEM focused image reconstruction that ASCE ATPases in viral dsDNA packaging motors adopt helical symmetry complementary to their dsDNA substrates. Together with previous data, including structural results showing these ATPases in planar ring conformations, our results suggest that these motors cycle between helical and planar cyclical symmetry, providing a possible mechanism for directional translocation of DNA. We further note that similar changes in quaternary structure have been observed for proteasome and helicase motors, suggesting an ancient and common mechanism of force generation that has been adapted for specific tasks over the course of evolution.

biophysics↗

bioRxiv2020

A DNA translocase operates by cycling between planarand lock-washer structures

Ring ATPases that translocate disordered polymers possess lock-washer architectures that they impose on their substrates during transport via a hand-over-hand mechanism. Here, we investigate the operation of ring motors that transport substrates possessing a preexisting helical structure, such as the bacteriophage {phi}29 dsDNA packaging motor. During each cycle, this pentameric motor tracks one helix strand (the tracking strand), and alternates between two segregated phases: a dwell in which it exchanges ADP for ATP and a burst in which it packages a full turn of DNA in four steps. We challenge this motor with DNA-RNA hybrids and dsRNA substrates and find that it adapts the size of its burst to the corresponding shorter helical pitches by keeping three of its power strokes invariant while shortening the fourth. Intermittently, the motor loses grip when the tracking strand is RNA, indicating that it makes load-bearing contacts with the substrate that are optimal with dsDNA. The motor possesses weaker grip when ADP-bound at the end of the burst. To rationalize all these observations, we propose a helical inchworm translocation mechanism in which the motor increasingly adopts a lock-washer structure during the ATP loading dwell and successively regains its planar form with each power stroke during the burst.

biophysics↗