Molecular motors on lipid bilayers and silicon dioxide: different driving forces for adsorption

Abstract

Understanding how different types of interactions govern adsorption of the myosin motor fragment heavy meromyosin (HMM) onto different substrates is important in functional studies of actomyosin and for the development of motor powered lab-on-a-chip applications. In this study, we have combined in vitro motility assays and quartz crystal microbalance with dissipation (QCM-D) monitoring to investigate the underlying adsorption mechanisms of HMM onto supported lipid bilayers in comparison with pure and silanized SiO₂. The QCM-D results, combined with data showing actin transportation by HMM adsorbed onto positively charged supported lipid bilayers, suggest reversible HMM surface adsorption via the negatively charged coiled-coil tail region. In contrast, the QCM-D data for HMM adsorption onto negatively charged lipids support a model according to which HMM adsorbs onto negatively charged surfaces largely via the positively charged actin binding regions. Adsorption studies at low (30–65 mM) and high (185–245 mM) ionic strengths onto piranha cleaned SiO₂ surfaces (contact angle < 20°) support this general model. However, unlike the situation for charged lipids, rinsing in high ionic strength solution caused only partial HMM desorption from SiO₂, without restoration of actin propulsion by the remaining HMM molecules. This suggests that mechanisms other than electrostatic interactions are involved in the tethering of HMM heads to SiO₂ surfaces. An expanded model for HMM adsorption is formulated on the basis of the data and the potential of the results for nanotechnological applications of actomyosin is discussed.