Biology subjects

Henn, A.

Publications and source records attributed to Henn, A..

3 recordsLinked to original sources

bioRxiv2025

Calcium-Regulated Mitochondria Remodeling by Myo19 is Required for Filopodia Tip-Extension

Mitochondria are highly adaptable organelles that change their shape, distribution, and movement to meet cellular needs. We investigate how EGF stimulation remodels mitochondrial behavior in human A431 carcinoma cells, where EGF suppresses proliferation but enhances calcium signaling and cell motility. EGF triggers mitochondrial fission, resulting in smaller, more mobile mitochondria that relocate to the tips of newly formed filopodia. Mitochondrial transport involves Kif5B (microtubule-based) and Myo19 (actin-based) motor proteins, which are regulated differently by calcium. EGF stimulation increases cytosolic calcium, weakening Kif5B-mediated transport and making Myo19 the primary transporter. Mitochondrial calcium uptake through the MCU channel is essential for redistribution, shape changes, and filopodia extension. Disrupting mitochondrial fission or calcium buffering impairs mitochondrial motility and the formation of filopodia. High-resolution imaging reveals the coordinated transport of mitochondria, involving fission, motor switching, and localized calcium signaling. We provide insights into how mitochondrial transport supports actin remodeling and protrusive activity, with implications for cell migration and therapies targeting mitochondrial-cytoskeletal interactions. HIGHLIGHTSO_LIEGF stimulation remodels the morphology of the mitochondrial network C_LIO_LIKif5B and Myo19 are required for mitochondrial motility C_LIO_LIMitochondria display two different velocities depending on the cell region C_LIO_LICalcium homeostasis contributes to mitochondrial network remodeling C_LI eTOC BLURBCell powerhouses called mitochondria can change shape and move within cells along tracks called the cytoskeleton. Stimulation of cells by stressors, such as growth factors, can generate signals that cause mitochondria to migrate to the cell edges using molecular motors. Importantly, this movement enables cells to form finger-like projections, providing the energy necessary for cell migration.

cell biology↗

bioRxiv2017

Auxiliary ATP binding sites power rapid unwinding by RecBCD

RecBCD, responsible for the initiation of double stranded break repair in bacteria, is a processive DNA helicase with an unwinding rate approaching [~]1,600 bp{middle dot}s-1. The mechanism enabling RecBCD to achieve such fast unwinding rate is not known. We employed a combination of equilibrium and time-resolved binding experiments, and ensemble and single molecule activity assays to uncover the molecular mechanism underlying RecBCDs rapid catalysis. We report the existence of auxiliary binding sites, where ATP binds with lower affinity and with distinct chemical interactions as compared to the known catalytic sites. The catalytic rate of RecBCD is reduced both by preventing and by strengthening ATP binding to these sites, suggesting that the dynamics of ATP at these sites modulates the enzymes rate. We propose a model by which RecBCD achieves its fast unwinding rate by utilizing the weaker binding sites to increase the flux of ATP to its catalytic sites.

biophysics↗

bioRxiv2017

RecBCD possesses strong coupling between DNA and nucleotides binding that may propel stepping mechanism during translocation

Double-strand DNA breaks are the severest type of genomic damage, requiring rapid response to ensure survival. RecBCD helicase in prokaryotes initiates processive and rapid DNA unzipping essential for break repair. Yet, the energetics of RecBCD during translocation along the DNA track needs to be quantitatively clarified. Specifically, its essential to understand how RecBCD switches between its binding states to enable its translocation. Here we determine, by systematic affinity measurements, the degree of coupling between DNA and nucleotide binding to RecBCD. We show that, in the presence of ADP, RecBCD binds weakly to DNA that harbors a double overhang mimicking an unwinding intermediate. Consistently, RecBCD binds weakly to ADP in the presence of the same DNA. We did not observe coupling between DNA and nucleotide binding for DNA molecules having only a single overhang, suggesting that RecBCD subunits must both bind DNA to "sense" the nucleotide state. Excitingly, we observed weak coupling for AMPpNp as RecBCD remains strongly bound to DNA in its presence. Detailed thermodynamic analysis of RecBCD reaction mechanism suggests an energetic compensation between RecB and RecD, which may be essential for rapid unwinding. Our findings provide the basis for a stepping mechanism during the processive translocation of RecBCD.

biochemistry↗