Use of a Quartz Crystal Microbalance for Studying the Effects of Propyl Gallate on the Interactions of Interleukin-6 and Its Soluble Receptor

Abstract

Quartz Crystal Microbalance (QCM) is known as a surface sensitive analytical device capable of on-line monitoring of interfacial reactions. To study the interaction between interleukin-6 (IL-6) and its soluble receptor (sIL-6R), as well as the effects of propyl gallate on IL-6/sIL-6R binding based on it, a QCM was employed to monitor the binding responses. In the experiments, sIL-6R was immobilized on the surface of QCM substrate, then different concentrations of IL-6 were added onto the substrate, respectively. The response frequency shift caused by the binding between IL-6 and sIL-6R was recorded. The results showed that sIL-6R was immobilized on the substrate surface with the density of 3.43 ng/mm2, IL-6 then bound to the immobilized sIL-6R specifically. FAST fit program was used to analyse the data obtained of the association of IL-6 and immobilized sIL-6R, fitting it to the biphasic kinetic equations. Kinetic constantsfor IL-6 binding to sIL-6R were determined from the plots of Kon versus the concentration of IL-6, kass=3.41×104 M-1 s-1, kdiss=1.80×10-2 s-1, thus, KD=5.28×10-7 M, KA=1.89×106 M-1. Furthermore, the effects of propyl gallate (PG) on interaction of IL-6 with sIL-6R were studied. The results showed that PG was able to enhance the binding between IL-6 and sIL- 6R. We propose that the interaction between IL-6 and sIL-6R is one of the targets which PG can act on in vivo. The QCM offers an effective way and a new clue to the study on the mechanism of propyl gallate at molecular level.