Hemocompatibility Enhancement through the Integration of the Antigenic Disguise Protein Tp0483 on a Material Surface

Matthew T. Dickerson, Dept. of Chemical Engineering, University of Kentucky, 177 F. Paul Anderson Tower, Lexington, KY 40506, Dr. Kimberly Anderson, Chemical Engineering, University of Kentucky, 177 F. Paul Anderson Tower, Lexington, KY 40506, and Dr. Leonidas Bachas, Chemistry, University of Kentucky, 207 Chemistry-Physics Building, Lexington, KY 40506.

The first response the body exhibits to a foreign material entering the bloodstream is rapid protein adhesion. Upon binding, adsorbed proteins undergo a conformation change which relays a signal to nearby platelets, resulting in platelet activation. Activated platelets adhere to the adsorbed proteins and at the same time secrete additional clotting factors that induce further platelet activation and result in the eventual formation of a thrombus on the surface. Thrombi pose many dangers including blood vessel occlusion as well as a heart attack or a stroke if the thrombus detaches from the material. To address this issue, it is of interest to develop new methods to improve hemocompatibility, one of these being exploitation of antigenic disguise proteins. Antigenic disguise refers to the property of specific pathogenic organisms to circumvent the body's immune system and avoid a host response. Treponema pallidum, the bacteria responsible for syphilis, is one example of this type of organism. T. pallidum has been known to exhibit latency periods of up to 50 years. It is hypothesized that this ability originates in several proteins presented on the surface of T. pallidum that exhibit the ability to bind host fibronectin (Fn). Fn is a common protein found throughout the body, and it is believed that by binding this protein, T. pallidum forms a protective coating that masks any potential antigenic targets from attack. One such T. pallidum protein is Tp0483, which serves as the focus of this research. In this study, the bond between Tp0483 and Fn as well as potential applications in increasing hemocompatibility are examined. Tp0483/Fn interactions were observed on various surface chemistries and hemocompatibility studies examining plasma protein adhesion and platelet activation were conducted. Binding studies utilized surface plasmon resonance (SPR) to view protein binding on functionalized self-assembled monolayers (SAM's) terminated in COOH, CH3, NH2, or OH. Results indicated that Tp0483 binds equally well to all surface chemistries, but only binds to Fn when immobilized on a COOH surface. This outcome suggests that Tp0483 possesses a wide range of diverse binding domains and that its conformation changes greatly based on the type of surface that it adsorbed to. As a result, the domain responsible for Fn binding is only exposed when Tp0483 is adsorbed on a negatively charged surface (COOH). Likewise, an RGD blocking study resulted in inhibition of Fn binding which supports previous studies indicating that the RGD peptide sequence on Fn mediates Tp0483 binding. Additionally, plasma protein binding studies demonstrated a decrease in binding to Tp0483/FN surfaces and platelet activation experiments showed a decrease in activation on these surfaces, both of which indicate improved hemocompatibility.