Conventional kinesin is routinely adsorbed to hydrophilic surfaces such as SiO(2). Pretreatment of surfaces with casein has become the standard protocol for achieving optimal kinesin activity, but the mechanism by which casein enhances kinesin surface adsorption and function is poorly understood. We used quartz crystal microbalance measurements and microtubule gliding assays to uncover the role that casein plays in enhancing the activity of surface-adsorbed kinesin. On SiO(2) surfaces, casein adsorbs as both a tightly bound monolayer and a reversibly bound second layer that has a dissociation constant of 500 nM and can be desorbed by washing with casein-free buffer. Experiments using truncated kinesins demonstrate that in the presence of soluble casein, kinesin tails bind well to the surface, whereas kinesin head binding is blocked. Removing soluble casein reverses these binding profiles. Surprisingly, reversibly bound casein plays only a moderate role during kinesin adsorption, but it significantly enhances kinesin activity when surface-adsorbed motors are interacting with microtubules. These results point to a model in which a dynamic casein bilayer prevents reversible association of the heads with the surface and enhances association of the kinesin tail with the surface. Understanding protein-surface interactions in this model system should provide a framework for engineering surfaces for functional adsorption of other motor proteins and surface-active enzymes.
Epoxide is one of the simplest functional groups on fullerenes, but mechanisms for migration of oxygen atoms and formations of CO and CO 2 gases upon heat treatment are still unclear. In this work, epoxidized fullerenes were heated in helium gas up to 673 K and the pyrolyzed structures of epoxidized fullerenes were analyzed using X-ray photoelectron spectroscopy, infrared spectroscopy, direct-injection mass spectrometry, elemental analysis, and density functional theory calculation. Functional groups such as CO and lactone groups were formed by heat treatment of the epoxidized fullerenes at 523 K. At 673 K, lactone groups were decomposed into CO and CO 2 gases. The amount of the CO 2 gas was more than that of the CO gas. This suggests that a formation of CO 2 gas from lactone groups is energetically more favorable than that of CO gas. Moreover, the ratio of CO 2 gas to CO gas increased, as the amount of oxygen atoms on fullerenes increased. The formation of CO and CO 2 gases at 673 K indicates that the presence of carbene sites with either vacancy defects or ether groups on fullerenes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.