Effects of Detergents on the Conformation of Escherichia coli tRNA as Measured by Circular Dichroism

Abstract

The effect of a cationic detergent, lauryl pyridiniumchloride (LPC), and an anionic one, sodium n-octylbenzenesulfonate (SOBS), on the conformation of unfractionated Escherichia coli tRNA was investigated at various molar ratios of detergent to tRNA (D/R) in the presence and absence of Mg²⁺ and Na⁺ ions by measuring the circular dichroism (CD) at 265nm and 340 nm, which reflects conformational change involving base pairs and/or base stacking, and the disymmetry in the vicinity of 4-thiouridylate (4-TU), respectively.
In the presence of Mg²⁺ and Na⁺ ions, the tRNA retains its native structure even in the presence of high molar ratios of detergent to tRNA (D/R_??_40 at 265nm and D/R_??_20 at 340 run). However, in the absence of these metal ions, the ellipticity at 340nm was very sensitive to LPC concentration and decreased from 5, 600 to nearly -1, 600 at 25°C with the increase of D/R ratios up to 20, and a similar decrease in the ellipticity at 340nm was observed on thermal denaturation. This result suggests that the local environment involving the 4-TU region might be readily influenced by LPC, reflecting a large conformational change. However, no effect was observed in the case of the SOBS: tRNA system. On the other hand, secondary base pairing and/or base stacking structure was virtually invariant on adding both LPC and SOBS even at high D/R ratios in the absence of Mg²⁺ and Na⁺ ions.