The promotion and suppression of DNA charge neutralization by the cosolute ectoine

Abstract

Ectoine, a cosolute and osmolyte, is used by extremophilic microorganisms to maintain an osmotic equilibrium of cells with their surrounding medium under conditions of extreme salinity or thermal and pressure stresses. It is also considered a protectant of biomolecules such as protein and DNA in cells. In the present study, we investigate its influence on DNA charge neutralization and compaction through dynamic light scattering (DLS), atomic force microscopy (AFM) and single molecular magnetic tweezers (MT). We found that ectoine can promote DNA charge neutralization induced by multivalent cations at mild cosolute concentration in solution. When the concentration of ectoine is high enough, however, a mixed effect of promotion and suppression can be found under the same ionic conditions. In this case, the electrophoretic mobility (EM) of DNA is promoted in the region of low cation concentration, while suppressed in the region of high counterionic concentration. The charge neutralization of DNA by ectoine is also related to DNA compaction. The promotion and suppression of DNA compaction by ectoine was observed by AFM imaging. The condensed structure of DNA becomes more compact and then loose once more with the increasing concentration of ectoine. Meanwhile, the condensing forces of DNA measured by magnetic tweezers shows the same trend as does the DNA EM. We explained the experimental findings through the combined effect of two intrinsic features of ectoine, preferential exclusion and enhancement of the dielectric constant of the medium. Fig. 1 Molecular structure of ectoine.

DNA–Lysozyme Nanoarchitectonics: Quantitative Investigation on Charge Inversion and Compaction

“…The process is always companied by DNA charge neutralization by the counterion [ 36 ]. When DNA is mixed with positively charged polyelectrolytes such as cationic polymers, polymerization formation or macrophase separation often occurs [ 21 ]. Since DNA is negatively charged in solution, the process of DNA compaction must overcome the electrostatic repulsion between segments of DNA so that one or few DNA chains can form a more compact and ordered structure.…”

“…In a previous mechanical measurement of DNA–lysozyme complexes in optical tweezers [ 1 ], they found that the persistence length of DNA–lysozyme complexes exhibits a nonmonotonic behavior as a function of the protein concentration. We have studied DNA complexes at various ionic and solution conditions in the past [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ].…”

Demonstration of pH-controlled DNA–surfactant manipulation for biomolecules

“…14,24 The procedure can be described briey as follows: a DNA chain is bound at one end to an immobile support (the glass sidewalls) and at the other end to a paramagnetic bead. [18][19][20][21] A permanent magnet controlled by a micromanipulator system (MP-285), Sutter Instruments (Novato, CA, USA) is used to exert a force on the paramagnetic bead to pull tethered DNA. The movement of paramagnetic bead was recorded by a CCD camera in real-time.…”