Biology subjects

Molloy, J. E.

Publications and source records attributed to Molloy, J. E..

7 recordsLinked to original sources

bioRxiv2026

Dynamic phosphorylation of the Plasmodium falciparum Myosin A motor regulates motor speed and is important for asexual replication

Malaria parasite invasion of red blood cells is powered by Myosin A (MyoA), the actomyosin motor which is a core component of the glideosome. Our previous phosphoproteomic study identified a cyclic GMP-dependent phosphorylation site on MyoA at Ser19, suggesting that cyclic nucleotide signalling may directly regulate motor activity during invasion. However, the functional significance of this phosphorylation site remains unclear. Here, we show that Plasmodium falciparum MyoA phosphorylation at Ser19 is dynamically regulated during the intraerythrocytic cycle, peaking in extracellular merozoites and rapidly declining following invasion. Using conditional depletion of MyoA, we show that MyoA is essential for red blood cell invasion but dispensable for gametocyte development. Conditional complementation with mutant versions of MyoA that either mimic (S19D) or ablate phosphorylation (S19A) reveal markedly impaired asexual parasite proliferation, highlighting the importance of precise regulation of MyoA phosphorylation at Ser19. In vitro motility assays using parasite-derived MyoA showed that ablating phosphorylation either pharmacologically or by introducing an S19A mutation, reduces motor speed. Conversely, introducing a phosphomimetic S19D mutation restores motility levels comparable to phosphorylated wild type MyoA. Collectively, these results establish MyoA Ser19 phosphorylation as a regulatory switch for actomyosin motor activity.

cell biology↗

bioRxiv2024

The eduWOSM: an advanced optical microscope for education

To improve access to advanced optical microscopy in educational and resource-limited settings we have developed the eduWOSM (educational Warwick Open Source Microscope), an open hardware platform for transmitted-light and epifluorescence imaging in up to 4 colours, including single molecule imaging. EduWOSMs are robust, bright, compact, portable and ultra-stable. They are controlled entirely by open source hardware and software, with an option for remote control from a webpage. Here we describe the core eduWOSM technology and benchmark its performance using 3 example projects, single fluorophore tracking of tubulin heterodimers within gliding microtubules, 4D (deconvolution) imaging/tracking of chromosome motions in dividing human cells, and automated single particle tracking in vitro and in live cells with classification into subdiffusive, diffusive and superdiffusive motion.

cell biology↗

bioRxiv2022

Characterization of Plasmodium falciparum myosin B in complex with the calmodulin-like domain of its light chain MLC-B

Myosin B (MyoB) is a class 14 myosin expressed in all invasive stages of the malaria parasite, Plasmodium falciparum. It is not associated with the glideosome complex that drives motility and invasion of host cells. During red blood cell invasion, it remains at the apical tip of the merozoite but is no longer observed once invasion is completed. MyoB is not essential for parasite survival but, when it is knocked out, merozoites are delayed in the initial stages of red blood cell invasion, giving rise to a growth defect that correlates with reduced invasion success. Here, we have expressed and purified functional MyoB with the help of parasite-specific chaperones Hsp90 and Unc45, characterized its binding to actin and its known light chain MLC-B using biochemical and biophysical methods, and determined its low-resolution structure in solution using small-angle X-ray scattering. In addition to MLC-B, four other putative regulatory light chains were found to bind to the MyoB IQ2 motif in vitro. The purified recombinant MyoB adopted the overall shape of a myosin, exhibited actin-activated ATPase activity, and moved actin filaments in vitro. The ADP release rate was faster than the ATP turnover number, and thus, does not appear to be rate-limiting. This, together with the observed high affinity to actin and the specific localization of MyoB, may point towards a role in tethering and/or force sensing during early stages of invasion.

biochemistry↗

bioRxiv2020

Single-molecule measurements reveal that PARP1 condenses DNA by loop formation

Poly(ADP-ribose) polymerase 1 (PARP1) is an abundant nuclear enzyme that plays important roles in DNA repair, chromatin organization and transcription regulation. Although binding and activation of PARP1 by DNA damage sites has been extensively studied, little is known about how PARP1 binds to long stretches of undamaged DNA and how it could shape chromatin architecture. Here, using a combination of single-molecule techniques including magnetic tweezers and atomic force microscopy, we show that PARP1 binds and condenses undamaged, kilobase-length DNA subject to sub-picoNewton mechanical forces. Decondensation by high force proceeds through a series of discrete increases in extension, indicating that PARP1 stabilizes loops of DNA. This model is supported by DNA braiding experiments which show that PARP1 can bind at the intersection of two separate DNA molecules. PARP inhibitors do not affect the level of condensation of undamaged DNA, but act to block condensation reversal for damaged DNA in the presence of NAD+. Our findings establish a mechanism for PARP1 in the organization of chromatin structure.

biophysics↗

bioRxiv2020

High-resolution structures of malaria parasite actomyosin and actin filaments

Malaria is responsible for half a million deaths annually and poses a huge economic burden on the developing world. The mosquito-borne parasites (Plasmodium spp.) that cause the disease depend upon an unconventional actomyosin motor for both gliding motility and host cell invasion. The motor system, often referred to as the glideosome complex, remains to be understood in molecular terms and is an attractive target for new drugs that might block the infection pathway. Here, we present the first high-resolution structure of the actomyosin motor complex from Plasmodium falciparum. Our structure includes the malaria parasite actin filament (PfAct1) complexed with the myosin motor (PfMyoA) and its two associated light-chains. The high-resolution core structure reveals the PfAct1:PfMyoA interface in atomic detail, while at lower-resolution, we visualize the PfMyoA light-chain binding region, including the essential light chain (PfELC) and the myosin tail interacting protein (PfMTIP). Finally, we report a bare PfAct1 filament structure at an improved resolution, which gives new information about the nucleotide-binding site, including the orientation of the ATP/ADP sensor, Ser15, and the presence of a channel, which we propose as a possible phosphate exit path after ATP hydrolysis.Significance statement We present the first structure of the malaria parasite motor complex; actin 1 (PfAct1) and myosin A (PfMyoA) with its two light chains. We also report a high-resolution structure of filamentous PfAct1 that reveals new atomic details of the ATPase site, including a channel, which may provide an exit route for phosphate and explain why phosphate release is faster in PfAct1 compared to canonical actins. PfAct1 goes through no conformational changes upon PfMyoA binding. Our PfMyoA structure also superimposes with a recent crystal structure of PfMyoA alone, though there are small but important conformational changes at the interface. Our structures serve as an excellent starting point for drug design against malaria, which is one of the most devastating infectious diseases.Competing Interest StatementThe authors have declared no competing interest.View Full Text

biophysics↗

bioRxiv2018

TorC2 dependent phosphorylation modulates calcium regulation of fission yeast myosin.

All cells have the ability to respond to changes in their environment. Signalling networks modulate cytoskeleton and membrane organisation to impact cell cycle progression, polarised cell growth and multicellular development according to the environmental setting. Using diverse in vitro, in vivo and single molecule techniques we have explored the role of myosin-1 signalling in regulating endocytosis during both mitotic and meiotic cell cycles. We have established that a conserved serine within the neck region of the sole fission yeast myosin-1 is phosphorylated in a TORC2 dependent manner to modulate myosin function. Myo1 neck phosphorylation brings about a change in the conformation of the neck region and modifies its interaction with calmodulins, Myo1 dynamics at endocytic foci, and promotes calcium dependent switching between different calmodulin light chains. These data provide insight into a novel mechanism by which myosin neck phosphorylation modulates acto-myosin dynamics to control polarised cell growth in response to mitotic and meiotic cell-cycle progression and the cellular environment.

cell biology↗

bioRxiv2018

Mechanics of CaMKII-actin networks

Calcium calmodulin dependent kinase (CaMKII) has an important role in dendritic spine remodelling upon synaptic stimulation. Using fluorescence video microscopy and image analysis, we investigated the architectural dynamics of rhodamine-phalloidin stabilized F-actin networks cross-linked by CaMKII. We used automated image analysis to identify F-actin bundles and cross-over junctions and developed a dimensionless metric to characterize network architecture. Similar networks were formed by three different CaMKII species with ten-fold length difference in the linker region between the kinase domain and holoenzyme hub; implying linker length is not a primary determinant of F-actin binding. Electron micrographs showed that, at physiological molar ratios, single CaMKII holoenzymes cross-linked multiple F-actin filaments in random networks, whereas at higher CaMKII / F-actin ratios filaments bundled. Light microscopy established that random networks resisted macromolecular crowding, with polyethylene glycol mimicking cytoplasmic osmolarity, and blocked ATP-powered compaction by myosin-2 mini-filaments. Importantly, the networks disassembled following addition of calcium calmodulin and were then rapidly spaced into compacted foci by myosin motors or, more slowly, aggregated by crowding. Single molecule TIRF microscopy showed CaMKII dissociation from surface-immobilized G-actin exhibited a mono-exponential dwell-time distribution, whereas CaMKII bound to F-actin networks had a long-lived fraction, trapped at cross-over junctions. Release of CaMKII from F-actin, triggered by calcium calmodulin did not require ATP (hence phosphorylation) and was too rapid to measure with video-rate imaging. The residual bound-fraction was reduced substantially upon addition of an NMDA receptor peptide analogue. These results provide mechanistic insights to CaMKII-actin interactions at the collective network and single molecule level. Our findings argue that CaMKII-actin networks in dendritic spines are stable enough to protect the basal network architecture against physical stress but once CaMKII is disengaged by calcium calmodulin and sequestered by receptors at the synapse; F-actin compaction by myosin motors stabilizes the expanded spine compatible with the recorded times.

biophysics↗