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Lang, Christian,Hiscock, Matthew,Larsen, Kim,Moffat, Jonathan,Sundaram, Ravi Korean Society of Microscopy 2015 Applied microscopy Vol.20 No.1
Here we show how by processing energy dispersive X-ray spectrometry (EDS) data obtained using highly sensitive, new generation EDS detectors in the AZtec LayerProbe software we can obtain data of sufficiently high quality to non-destructively measure the number of layers in two-dimensional (2D) $MoS_2$ and $MoS_2/WSe_2$ and thereby enable the characterization of working devices based on 2D materials. We compare the thickness measurements with EDS to results from atomic force microscopy measurements. We also show how we can use electron backscatter diffraction (EBSD) to address fabrication challenges of 2D materials. Results from EBSD analysis of individual flakes of exfoliated $MoS_2$ obtained using the Nordlys Nano detector are shown to aid a better understanding of the exfoliation process which is still widely used to produce 2D materials for research purposes.
Nucleotide-dependent control of internal strains in ring-shaped AAA+ motors.
Hwang, Wonmuk,Lang, Matthew J SPRINGER SCIENCE + BUSINESS MEDIA 2013 Cellular and molecular bioengineering Vol.6 No.1
<P>The AAA+ (ATPase Associated with various cellular Activities) machinery represents an extremely successful and widely used design plan for biological motors. Recently found crystal structures are beginning to reveal nucleotide-dependent conformational changes in the canonical hexameric rings of the AAA+ motors. However, the physical mechanism by which ATP binding on one subunit allosterically propagates across the entire ring remains to be found. Here we analyze and compare structural organization of three ring-shaped AAA+ motors, ClpX, HslU, and dynein. By constructing multimers using subunits of identical conformations, we find that individual subunits locally possess helical geometries with varying pitch, radius, chirality, and symmetry number. These results suggest that binding of an ATP to a subunit imposes conformational constraint that must be accommodated by more flexible nucleotide-free subunits to relieve mechanical strain on the ring. Local deformation of the ring contour and subsequent propagation of strains may be a general strategy that AAA+ motors adopt to generate force while achieving functional diversity.</P>
A new physical interpretation of optical and infrared variability in quasars
Ross, Nicholas P,Ford, K E Saavik,Graham, Matthew,McKernan, Barry,Stern, Daniel,Meisner, Aaron M,Assef, Roberto J,Dey, Arjun,Drake, Andrew J,Jun, Hyunsung D,Lang, Dustin Oxford University Press 2018 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.480 No.4
Kinesin-12 Kif15 Targets Kinetochore Fibers through an Intrinsic Two-Step Mechanism
Sturgill, Emma G.,Das, D.,Takizawa, Y.,Shin, Y.,Collier, Scott E.,Ohi, Melanie D.,Hwang, W.,Lang, Matthew J.,Ohi, R. Current Biology Ltd ; Elsevier Science Ltd 2014 Current biology Vol.24 No.19
Proteins that recognize and act on specific subsets of microtubules (MTs) enable the varied functions of the MT cytoskeleton. We recently discovered that Kif15 localizes exclusively to kinetochore fibers (K-fibers) [1, 2] or bundles of kinetochore-MTs within the mitotic spindle. It is currently speculated that the MT-associated protein TPX2 loads Kif15 onto spindle MTs [3-5], but this model has not been rigorously tested. Here, we show that Kif15 accumulates on MT bundles as a consequence of two inherent biochemical properties. First, Kif15 is self-repressed by its C terminus. Second, Kif15 harbors a nonmotor MT-binding site, enabling dimeric Kif15 to crosslink and slide MTs. Two-MT binding activates Kif15, resulting in its accumulation on and motility within MT bundles but not on individual MTs. We propose that Kif15 targets K-fibers via an intrinsic two-step mechanism involving molecular unfolding and two-MT binding. This work challenges the current model of Kif15 regulation and provides the first account of a kinesin that specifically recognizes a higher-order MT array.
The nesprin-cytoskeleton interface probed directly on single nuclei is a mechanically rich system
Balikov, Daniel A.,Brady, Sonia K.,Ko, Ung Hyun,Shin, Jennifer H.,de Pereda, Jose M.,Sonnenberg, Arnoud,Sung, Hak-Joon,Lang, Matthew J. TaylorFrancis 2017 Nucleus Vol.8 No.5
<P>The cytoskeleton provides structure and plays an important role in cellular function such as migration, resisting compression forces, and transport. The cytoskeleton also reacts to physical cues such as fluid shear stress or extracellular matrix remodeling by reorganizing filament associations, most commonly focal adhesions and cell-cell cadherin junctions. These mechanical stimuli can result in genome-level changes, and the physical connection of the cytoskeleton to the nucleus provides an optimal conduit for signal transduction by interfacing with nuclear envelope proteins, called nesprins, within the LINC (linker of the nucleus to the cytoskeleton) complex. Using single-molecule on single nuclei assays, we report that the interactions between the nucleus and the cytoskeleton, thought to be nesprin-cytoskeleton interactions, are highly sensitive to force magnitude and direction depending on whether cells are historically interfaced with the matrix or with cell aggregates. Application of approximate to 10-30 pN forces to these nesprin linkages yielded structural transitions, with a base transition size of 5-6nm, which are speculated to be associated with partial unfoldings of the spectrin domains of the nesprins and/or structural changes of histones within the nucleus.</P>
Collective Force Regulation in Anti-parallel Microtubule Gliding by Dimeric Kif15 Kinesin Motors
Reinemann, Dana N.,Sturgill, Emma G.,Das, Dibyendu Kumar,Degen, Miriam Steiner,Vö,rö,s, Zsuzsanna,Hwang, Wonmuk,Ohi, Ryoma,Lang, Matthew J. Elsevier 2017 Current Biology Vol.27 No.18
<P><B>Summary</B></P> <P>During cell division, the mitotic kinesin-5 Eg5 generates most of the force required to separate centrosomes during spindle assembly. However, Kif15, another mitotic kinesin, can replace Eg5 function, permitting mammalian cells to acquire resistance to Eg5 poisons. Unlike Eg5, the mechanism by which Kif15 generates centrosome separation forces is unknown. Here we investigated the mechanical properties and force generation capacity of Kif15 at the single-molecule level using optical tweezers. We found that the non-motor microtubule-binding tail domain interacts with the microtubule’s E-hook tail with a rupture force higher than the stall force of the motor. This allows Kif15 dimers to productively and efficiently generate forces that could potentially slide microtubules apart. Using an in vitro optical trapping and fluorescence assay, we found that Kif15 slides anti-parallel microtubules apart with gradual force buildup while parallel microtubule bundles remain stationary with a small amount of antagonizing force generated. A stochastic simulation shows the essential role of Kif15’s tail domain for load storage within the Kif15-microtubule system. These results suggest a mechanism for how Kif15 rescues bipolar spindle assembly.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Kif15 transports microtubules in bundles through motor and non-motor coordination </LI> <LI> Kif15’s non-motor microtubule-binding site (Coil-1) is stronger than stall force </LI> <LI> Kif15 generates force in anti-parallel bundles and has a force-feedback mechanism </LI> <LI> Coil-1 tethering is needed for the force ramp and plateau in anti-parallel bundles </LI> </UL> </P>