Johannes Kepler University in Linz Austria has published a High-Speed Atomic Force Microscopy video of human lectin CLEC4G binding to glycans on a SARS-CoV-2 spike. This video was recorded by Daniel Canena and Peter Hinterdorfer and is, according to the two researchers, the first short film of the active structure the virus uses to attach to cell
The current pandemic is not the only health threat worldwide. Another worry is the increasing antibiotic resistance which increases the fear to run out of effective antibiotics.
This is one of the reasons why antimicrobial peptides (AMPs) are gaining more and more interest.
The lipopeptide Daptomycin ( DAP ) has been therapeutically used as a last resort antibiotic against multidrug-resistant enterococci and staphylococci in the past. Unfortunately, some strains have become resistant to Dap in recent years. There still is a knowledge-gap on the details of Dap activity. It is therefore important to understand the structure-activity relationships of AMPs on membranes in order to develop more antibiotics of this type as a countermeasure to the spread of resistance.*
High Speed Atomic Force Microscopy ( HS-AFM ) makes it possible to observe dynamic biological processes on a molecular level.
In the article “High-speed atomic force microscopy highlights new molecular mechanism of daptomycin action” Francesca Zuttion, Adai Colom, Stefan Matile, Denes Farago, Frédérique Pompeo, Janos Kokavecz, Anne Galinier, James Sturgis and Ignacio Casuso describe how, by using the possibilities offered by high speed atomic force microscopy, they were able to confirm some up until now hypothetical models and additionally detected some previously unknown molecular mechanisms. *
The HS-AFM imaging made it possible for the authors to observe the development of the dynamics of interaction at the molecular-level over several hours. *
They investigated the lipopeptide Daptomycin under infection-like conditions and could confirm Dap oligomerization and the existence of half pores. *
They also mimicked bacterial resistance conditions by increasing the CL-content in the membrane. *
By correlating the results of other research techniques such as FRET, SANS, NMR, CD or electrophysiology techniques with the results they achieved with high speed atomic force microscopy F. Zuttion et al. were able to confirm several, previously, hypothetical models, and detect several unknown molecular mechanisms. *
It is to be hoped that the possibilities offered by HS-AFM imaging will stimulate new models and insight on the structure-activity relationship of membrane-interacting molecules and also open up the possiblity to increase the throughput of screening of molecular candidates considerably. *
NanoWorld USC ( Ultra-Short AFM Cantilevers) of the USC-F1.2-k0.15 type, which are specially designed for the use in high speed atomic force microscopy, were used for the HS-AFM imaging described in the article cited below. These AFM probes have a typical resonance frequency of 1200 kHz and have a wear resistant AFM tip made from high density carbon.
Figure 4 Sub-MIC Dap on POPG at 37 °C. Tens of minutes from “High-speed atomic force microscopy highlights new molecular mechanism of daptomycin action” by Francesca Zuttion et al. Intermediate stages a A new structure appeared: dimples, zones of thinner membrane thickness, whose diameter was in the range 7 ± 2 nm. Most dimples diffuse, but some remained static (colour scale: 3 nm). Movie details: frame rate 97 ms; zoom of a full image of 150 nm × 90 nm and 256 × 160 pixels. b The dimple diffusion consisted of swinging trajectories, implying membrane-mediated dimple-dimple attraction (colour scale: 3 nm). b, right, Energy profile of the interaction of the dimples obtained derived from 120 centre-to-centre distance measurements that contains as the oligomers two energy minima. Movie details: frame rate 83 ms; full image of 150 nm × 150 nm and 256 × 256 pixels. c In some membrane zones, clusters of dimples, reminiscent of cubic phases, developed (colour scale: 4 nm). Movie details: frame rate 74 ms; full image of 90 nm × 60 nm and 256 × 160 pixels. d The clusters of dimples were moderately dynamical in time, with moderate internal rearrangements (colour scale: 4 nm). Movie details: frame rate 74 ms; full image of 25 nm × 16 nm and 256 × 160 pixels. e The other deformation found was elongated-humps on top of the POPG membrane. e, left, An elongated-hump in the proximity of a cluster of dimples (colour scale: 4 nm). e, right, A close-up and a profile of an elongated-hump. Additional images of elongated-humps on Supplementary Fig. 1. Movie details: frame rate 479 ms; zoom of full image of 250 nm × 200 nm and 300 × 256 pixels. f It was observed that the dimples and the elongated-humps fused and gave yield to pores of toroidal structure where a protruding ring surrounds the pore (colour scale: 4 nm). Movie details: frame rate 74 ms; full image of 40 nm × 40 nm and 256 × 160 pixels.
*Francesca Zuttion, Adai Colom, Stefan Matile, Denes Farago, Frédérique Pompeo, Janos Kokavecz, Anne Galinier, James Sturgis and Ignacio Casuso High-speed atomic force microscopy highlights new molecular mechanism of daptomycin action Nature Communications volume 11, Article number: 6312 (2020) DOI: https://doi.org/10.1038/s41467-020-19710-z
Open Access : The article “High-speed atomic force microscopy highlights new molecular mechanism of daptomycin action” by Francesca Zuttion, Adai Colom, Stefan Matile, Denes Farago, Frédérique Pompeo, Janos Kokavecz, Anne Galinier, James Sturgis and Ignacio Casuso is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.
Excitatory amino acid transporters (EAATs) are important in many physiological processes and crucial for the removal of excitatory amino acids from the synaptic cleft.*
In the article “Millisecond dynamics of an unlabeled amino acid transporter “ Tina R. Matin, George R. Heath, Gerard H. M. Huysmans, Olga Boudker and Simon Scheuring develop and apply high-speed atomic force microscopy line-scanning (HS-AFM-LS) combined with automated state assignment and transition analysis for the determination of transport dynamics of unlabeled membrane-reconstituted GltPh, a prokaryotic EAAT homologue, with millisecond temporal resolution.*
Among the bulk and single-molecule techniques, high-speed atomic force microscopy ( HS-AFM ) stands out with its ability to provide real-time structural and dynamical information of single molecules. HS-AFM images label-free molecules under close-to-physiological conditions with ~0.1 nm vertical and ~1 nm lateral imaging resolution. Furthermore, HS-AFM has typically ~100 ms temporal resolution, giving access to structure–dynamics relationship of proteins, though the achievable imaging speed depends on sample characteristics like scan size and surface corrugation.
Recently in a quest to achieve higher temporal resolutions, the authors of the cited article used HS-AFM line scanning (HS-AFM-LS) for the analysis of single-protein dynamics. *
Line scanning, using a conventional AFM, has been used to study protein–protein interactions earlier. In HS-AFM-LS, the slow-scan axis (y-direction) is disabled. Therefore, instead of imaging an x/y-area, the scientists scan over one horizontal x-line several hundreds to thousands of times per second, thus reaching millisecond temporal resolution. The topographical readouts of this line are stacked one after another, resulting in kymographs of the dynamical behavior of the molecules. Therefore, HS-AFM-LS has between 2 and 3 orders of magnitude higher temporal resolution than HS-AFM imaging and should allow the detection of fast transporter dynamics and possible intermediate states that have so far escaped kinetic characterization. *
All AFM images presented in this study were taken using a HS-AFM operated in amplitude modulation mode (with typical free and setpoint amplitudes, Afree = 1.0 nm and Aset = 0.9 nm, respectively using optimized scan and feedback parameters. NanoWorld Ultra-Short Cantilevers ( NanoWorld’s AFM probe series especially dedicated for High Speed Scanning) of the USC-F1.2-k0.15 type were used. In the presented experiments, four different buffer conditions were used. *
As the authors state in their article they find that GltPh transporters can operate much faster than previously reported, with state dwell-times in the 50 ms range, and report the kinetics of an intermediate transport state with height between the outward- and inward-facing states. Transport domains stochastically probe transmembrane motion, and reversible unsuccessful excursions to the intermediate state occur. The presented approach and analysis methodology are generally applicable to study transporter kinetics at system-relevant temporal resolution.*
Figure 2 from “Millisecond dynamics of an unlabeled amino acid transporter” by Tina R. Matin et al. HS-AFM line scanning (HS-AFM-LS): millisecond temporal resolution of unlabeled transporter dynamics.: a HS-AFM image of a membrane packed with GltPh exposing the extracellular face before HS-AFM-LS (apo condition: 20 mM Tris-HCl, pH7.5, 150 mM KCl). Dashed lines indicate the position of the central scan line where subsequent HS-AFM-LS is performed. b Six seconds of a HS-AFM-LS kymograph with 3.3 ms line acquisition speed. Each transporter domain appears as a vertical line. c Projection (top) and height profile (bottom) of b. d HS-AFM image after HS-AFM-LS. The lateral position of recognizable features in a–d are indicated by arrowheads. e One second high-magnification views of dashed regions 1, 2, and 3 in b. Transport domain excursions to the inward-facing state appear as dark dwells along the vertical time axis. f Projection (top) and height profile (bottom) of e. Arrowheads indicate the position of the seven protomers in the kymograph (red: active protomer #5). g Height/time traces (gray) and state fits (red) of the active domain (protomer #5) in e. This figure is representative of the experimental sequence for the >50 replicates analyzed in this work.
*Tina R. Matin, George R. Heath, Gerard H. M. Huysmans, Olga Boudker and Simon Scheuring Millisecond dynamics of an unlabeled amino acid transporter Nature Communications volume 11, Article number: 5016 (2020) DOI: https://doi.org/10.1038/s41467-020-18811-z
Open Access : The article “Millisecond dynamics of an unlabeled amino acid transporter” by Tina R. Matin, George R. Heath, Gerard H. M. Huysmans, Olga Boudker and Simon Scheuring is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.
