Nucleosome liquid crystal

Nucleosome-nucleosome interaction potentials can be calibrated by comparison with the characteristics of liquid crystals of mononucleosomes at high concentrations. Under suitable conditions, nucleosome core particles form a hexagonal-columnar phase with a distance of 11.55 1 nm between the columns and a mean distance of 7.16 0.65 nm between the particles in one column [44,46]. These distances may be assumed to correspond to the positions of the minima of an attractive internucleosomal potential. The depth of the interaction potential (i.e., the binding energy per nucleosome) was estimated in the stretching experiments of Cui and Bustamante [66] to 2.6-3.4 kT. A slightly lower potential minimum of 1.25 kT is obtained by a comparison of the stability of the nucleosome liquid crystal phase with simulations [50]. 

The interaction between nucleosomes plays an important role for the stability of the 30 nm fiber recent experiments on liquid crystals of mononucleosomes [44-47] and also less concentrated mononucleosome solutions [48,49] show an attractive interaction that can be parameterized by an anisotropic Leonard-Jones type potential [50]. Also, an electrostatic interaction potential has been computed using the crystallographic structure of the nucleosome [51]. The influence of these potentials on the structure of the fiber is discussed below together with the corresponding models. 

An important addition compared to previous models was the parameterization of the internucleosomal interaction potential in the form of an anisotropic attractive potential of the Lennard-Jones form, the so-called Gay-Berne potential [90]. Here, the depth and location of the potential minimum can be set independently for radial and axial interactions, effectively allowing the use of an ellipsoid as a good first-order approximation of the shape of the nucleosome. The potential had to be calibrated from independent experimental data, which exists, e.g., from the studies of mononucleosome liquid crystals by the Livolant group [44,46] (see above). The position of the potential minima in axial and radial direction were obtained from the periodicity of the liquid crystal in these directions, and the depth of the potential minimum was estimated from a simulation of liquid crystals using the same potential. 

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See also in sourсe #XX -- [ , , ]

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