Micromechanical Study of Hyperacetylated Nucleosomes Using Single Molecule Transverse Magnetic Tweezers

Abstract

Nucleosomes are stable complexes of DNA and histone proteins that are essential for the proper functioning of the genome. These structures must be unwrapped and disassembled for processes such as gene expression, replication, and repair. Histone post-translational modifications (PTMs) are known to play a significant role in regulating the structural changes of nucleosomes. However, the underlying mechanisms by which these modifications function remain unclear. In this study, we report the results of single molecule micromanipulation experiments on DNA–protein complexes composed of hyperacetylated histone proteins using transverse magnetic tweezers. The experiments were conducted by pre-extending λ-DNA with a force less than 4 pN before introducing hyperacetylated histones into the sample chamber. The DNA shortened as the histones formed complexes with it and the nucleosome arrays were then exposed to increasing tension, resulting in quantized changes in the DNA’s extension with step sizes of (integral multiples of) ~50 nm. We also compared results of experiments using PTM histones and native histones with data collected for both types of histones for the same force ranges (2–80 pN) and loading rates. Our data show that hyperacetylated nucleosomes require an unbinding force of around ~2.5 pN, which is similar to that required for native histones. Moreover, we identified clear differences between the step-size distributions of native and hyperacetylated histones and found that in contrast to tethers reconstituted with native histones, the majority of nucleosomes in tethers compacted with hyperacetylated histones underwent disassembly at forces significantly lower than 6 pN.

Receptor–Ligand Binding: Effect of Mechanical Factors

“…It is widely recognized that mechanical factors are essential regulators of various cellular processes, including cell adhesion, migration, growth, and differentiation [18][19][20][21][22][23], and thus are implicated in regulating relevant physiological and pathological activities [24][25][26]. The ever-developing advancement in biomechanical tools and methods further enables us to study the response of receptor-ligand binding to the mechanical stimuli at the molecular level [27][28][29][30][31][32], and new insights into the role of mechanical factors in the in situ receptor-ligand interactions are rapidly emerging [33,34]. For example, except for the ideal bonds that are insensitive to mechanical stress, two modes of mechanical regulation of binding have been proposed.…”