159 research outputs found
Carbon fibre tips for scanning probe microscopy based on quartz tuning fork force sensors
We report the fabrication and the characterization of carbon fibre tips for
their use in combined scanning tunnelling and force microscopy based on
piezoelectric quartz tuning fork force sensors. We find that the use of carbon
fibre tips results in a minimum impact on the dynamics of quartz tuning fork
force sensors yielding a high quality factor and consequently a high force
gradient sensitivity. This high force sensitivity in combination with high
electrical conductivity and oxidation resistance of carbon fibre tips make them
very convenient for combined and simultaneous scanning tunnelling microscopy
and atomic force microscopy measurements. Interestingly, these tips are quite
robust against occasionally occurring tip crashes. An electrochemical
fabrication procedure to etch the tips is presented that produces a sub-100 nm
apex radius in a reproducible way which can yield high resolution images.Comment: 14 pages, 10 figure
Structural basis of nucleosome assembly by the Abo1 AAA+ ATPase histone chaperone
The fundamental unit of chromatin, the nucleosome, is an intricate structure that requires histone chaperones for assembly. ATAD2 AAA+???ATPases are a family of histone chaperones that regulate nucleosome density and chromatin dynamics. Here, we demonstrate that the fission yeast ATAD2 homolog, Abo1, deposits histone H3???H4 onto DNA in an ATP-hydrolysis-dependent manner by in vitro reconstitution and single-tethered DNA curtain assays. We present cryo-EM structures of an ATAD2 family ATPase to atomic resolution in three different nucleotide states, revealing unique structural features required for histone loading on DNA, and directly visualize the transitions of Abo1 from an asymmetric spiral (ATP-state) to a symmetric ring (ADP- and apo-states) using high-speed atomic force microscopy (HS-AFM). Furthermore, we find that the acidic pore of ATP-Abo1 binds a peptide substrate which is suggestive of a histone tail. Based on these results, we propose a model whereby Abo1 facilitates H3???H4 loading by utilizing ATP
Advanced Instrumentation of Frequency Modulation AFM for Subnanometer-Scale 2D/3D Measurements at Solid-Liquid Interfaces
Since the first demonstration of true atomic-resolution imaging by frequency modulation atomic force microscopy (FM-AFM) in liquid, the method has been used for imaging subnanometer-scale structures of various materials including minerals, biological systems and other organic molecules. Rencetly, there have been further advancements in theFM-AFMinstrumentation. Three-dimensional (3D) force measurement techniques are proposed for visualizing 3D hydration structures formed at a solid-liquid interface. Thesemethods further enabled to visualize 3D distributions of flexible surface structures at interfaces between soft materials andwater. Furthermore, the fundamental performance such as force sensitivity and operation speed have been significantly improved using a small cantilever and high-speed phase detector. These technical advancements enabled direct visualization of atomic-scale interfacial phenomena at 1 frame/s. In this chapter, these recent advancements in the FM-AFM instrumentation and their applications to the studies on various interfacial phenomena are presented. © Springer International Publishing Switzerland 201
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