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Biophysics question on Biological Magnets

  1. Dec 7, 2015 #1
    Hi,

    I have been reading this fascinating paper here:

    http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html

    I'm struggling with some of the biophysics, and it would be great to get a discussion going. In particular, I was struggling with the statements where it says "The two kinks appearing around zero magnetization indicate the existence of two vortex states with opposite directions, similar to the behaviours observed in ferrimagnetic nanoringshttp://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#ref54, and in agreement with the here proposed ‘iron-loop’ hypothesis on the basis of structural modelling"

    And also "We propose two possible causes of the intrinsic magnetic feature of this magnetosensor: the linear array of iron atoms and/or a synchronized circular current in the iron loops. To our knowledge, such ferrimagnetic behaviour and vortex states with opposite directions of the clCry4/clMagR protein complex in solution have not been shown previously, and are consistent with our observations"

    Can someone translate this into biologist-friendly terms, and expound on the ramifications of this? Thanks.
     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Dec 7, 2015 #2
    that link does not go to the paper but to a pay wall blocking the article (but giving the abstract). Can you provide an image of the magnetization in which the articles says are the "kinks"?
     
  4. Dec 8, 2015 #3
    OK, here's the full paragraph: "As complicated as biological systems are, they certainly obey and often make ingenious use of physical principles. To explore the physical properties of the protein-based nanostructured Cry/MagR complex, magnetic measurements of clCry4/clMagR (http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#f5 and http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#supplementary-information) were conducted with a commercial magnetometer (Quantum Design magnetic property measurement system, MPMS-XL1). http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#f5 reveals the field dependence of the magnetization of the clCry4/clMagR complex. The complex we identified is ferrimagnetic at room temperature, with a coercivity of approximately 20G in magnitude. The two kinks appearing around zero magnetization indicate the existence of two vortex states with opposite directions, similar to the behaviours observed in ferrimagnetic nanoringshttp://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#ref54, and in agreement with the here proposed ‘iron-loop’ hypothesis on the basis of structural modelling (http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#f3). In contrast, ferritin, the main intracellular storage form of iron, a spherical protein composed of 24 subunits, fully loaded with around 4,500 iron atoms, shows a linear dependence and no hysteresis in our experiment (http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#f5 and http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#supplementary-information), indicating a non-ferrimagnetic character consistent with previous reportshttp://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#ref55. We propose two possible causes of the intrinsic magnetic feature of this magnetosensor: the linear array of iron atoms and/or a synchronized circular current in the iron loops. To our knowledge, such ferrimagnetic behaviour and vortex states with opposite directions of the clCry4/clMagR protein complex in solution have not been shown previously, and are consistent with our observations (http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#f5)."


    Fig3:

    http://www.nature.com/nmat/journal/vaop/ncurrent/images_article/nmat4484-f3.jpg
    a,b, MagR assembled as a rod-like structure. Side (a) and top (b) views of a double-helical arrangement of 20 MagR molecules, and comparison between EM structure (left) and molecular model (right). Dotted boxes show one MagR monomer (yellow) and four MagR molecules (yellow and orange) comprising a disk-like unit (black), with four Fe–S clusters in the middle forming an iron loop. MagR molecules are coloured yellow and orange to emphasize the double-helical assembly. c,d, The complete structural model of the Cry/MagR magnetosensor. Side (c) and top (d) views of the magnetosensor, with ten Cry molecules (cyan) fully loaded to the MagR core (yellow). Comparisons between molecular model (right), light-dependent biocompass model (upper left) and EM structure (lower left) are shown. FADs in Cry are shown as blue sticks and Fe–S clusters in MagR are shown as spheres. The ‘iron-loop’ structures of the Fe–S cluster arrangement are highlighted with dashed black ovals in c. e, Proposed structural dynamics (detailed, top; coarse-grained, middle) based on the molecular model and EM structure of the magnetosensor. MagR is coloured yellow and orange to emphasize the double-helical assembly. Five Cry molecules are coloured cyan, with the magenta dotted line showing that the Cry molecules are helically located on the outer layer. The conserved helix–helix interactions between Cry and MagR are coloured red and grey in MagR, and blue in Cry. Four typical EM averages (bottom) exemplify the dynamics of Cry binding to MagR.


    Fig5:
    http://www.nature.com/nmat/journal/vaop/ncurrent/images_article/nmat4484-f5.jpg


    Representative raw image of the clCry4/clMagR magnetosensor complex prepared under the geomagnetic field (0.4G, or 0.04mT). Isolated rod-like particles aligned in parallel, vertical or other intermediate directions with respect to the geomagnetic direction are shown in red boxes, blue boxes and yellow circles, respectively. The definition of parallel, vertical and others is explained in b (insert). b, The percentage of isolated magnetosensor particles in the three directions corresponding to the geomagnetic field (0.4G, or 0.04mT) or to an enhanced external magnetic field (MF) (10G, or 1mT). The enhanced external magnetic field is applied vertically to the geomagnetic field. Around 500 particles are randomly picked using EMAN and analysed for each experiment. Results are from three independent experiments; error bars: mean ± s.d. c, clMagR (SDS–PAGE, left) and clCry4/clMagR complex (SDS–PAGE, right) can be enriched with iron beads from co-expressed cell lysis by a simple procedure. d, Magnetosensor protein crystals exhibited strong intrinsic magnetic polarity and rotated in synchrony with the external magnetic field. Two types of protein crystals, brown-to-black crystal (upper panels) and translucent yellowish crystals (lower panels) are shown. There is only one brown-to-black crystal in one hanging drop, which might be due to the merging of small crystals because of the magnetic dragging force; however, many translucent yellowish crystals may coexist. e, Magnetic properties of the clCry4/clMagR magnetosensor complex. Room-temperature magnetization as a function of the field for the clCry4/clMagR magnetosensor complex was obtained by subtracting the contribution of buffer from solution (http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4484.html#supplementary-information). The presence of a hysteresis loop indicates the ferrimagnetic behaviour of the clCry4/clMagR complex. f, Magnetic properties of synthesized magnetite-containing human ferritin (M-HFn) nanoparticles were used as a control. The linear dependence indicates that no ferrimagnetic ordering exists in M-HFn.

    upload_2015-12-8_4-56-1.png
     

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