Surfactant-Induced Conformational Change in Porcine Brain Calmodulin

Abstract

The conformational change of porcine brain calmodulin (CaM) with several surfactants has been investigated by using fluorescence spectra and circular dichroism (CD) measurements. Nonionic surfactants such as Tween 20, Tween 40, Tween 80, and Triton X100 had little effect on the conformation of CaM. Drastic conformational change of CaM was observed when anionic surfactants sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) were added. Addition of 1 mM SDS increased α-helical content of CaM both in the presence and the absence of Ca2+, and the α-helical content was 42% in the presence of Ca2+. When SDBS was added, the α-helical content of CaM decreased with increasing the surfactant concentration. At high SDBS concentration (12 mM) the CD spectrum was typical of a random coil both in the presence of Ca2+ and in its absence. Addition of the cationic benzalkonium chloride enhanced the breaking of an ordered conformation with a weak denaturation. These facts were supported by the results of fluorescence spectroscopy. © 1985, The Society of Polymer Science, Japan. All rights reserved.