X-ray Reflectivity on Fibronectin Binding on Charged Lipid Bilayers

In nature, fibronectin (FN) is known to form extended fiber networks when binding to specific receptors on cellular membranes as a major component of extracellular matrix (ECM) under an anionic environment of proteoglycans (PGs). Seeking to associate this phenomenon with a charge-specific reaction, many researchers have attempted to mimic an anionic system of PGs, and some have observed the same effects. As a part of the aligning efforts, we opted to use a negatively charged, supported lipid bilayer as a model membrane, and we studied the adsorption of FN by using X-ray reflectivity (XRR), through which we were able to study as a function of time the changes in the molecular structure of each compartment sectioned by using a specific model. We observed a noticeable increase in outer membrane thickness over time, with the roughness evolving across the membrane. This suggests that FN is attached to the model membrane in a brush-like form. In this paper, we describe the specific process underlying this behavior, which will provide profound insight into how the presence of negative charges affects the binding phenomena of FN, eventually providing a hint to understanding the fibrillogenesis mechanism of ECM.