Single-molecule Force Sepctroscopy Study On Dopa Adhesion

Dopa is a special kind of amino acid which is part of mussel foot protein. It has been found that all kinds of proteins in the mefp family contain dopa. There are three proteins which are dopa rich, mefp-1,-3,-5, with typically15-30mol%. Mefp-3,-5are found in the interface of the mussel foot plaque and the substratum. They are related with the ability of adhesion of mussel byssus. Mefp-1form the byssus thread which has the function of protection. Research found that mussel byssus adhesiveness is highly depended on the dopa ratio. In prior studies, rarely research dopa in single molecule level. With the revolutionary advances in instrument and detection means, single molecule force spectroscopy techniques have developed rapidly. Atomic force microscopy-based single molecule force spectroscopy method has been widely used in the intramolecular and intermolecular interactions, and generates a lot of important research results.In Chapter Two, we measured the interaction between dopa and three different substrates, Ti, SiO2and mica. First we synthesized Boc-dopa through organic chemistry method. Then we modified Boc-dopa on the tips which have PEG on the surface. Then we began the single molecular force spectrum experiment. The results show that the interaction forces between dopa and the three substrates are similar and are about200pN. We could tell that the dopa-substrate interaction is likely the same as mechanical proteins’ unfolding force. The interaction is very stable and not easy to break. Our result is useful for the design of functional materials.We found the limitation of the method which we used in the second chapter. So, in the third chapter, we report a new method which is more practical and efficient to study interactions between molecules. We choose a rigid polysaccharide, HA, as the polymer backbone in the new method. We first modified ligand on the HA backbone. And drop the modified HA solution on the substrate with receptor fixed on the surface. As the ligand on the HA would combine with the receptor. We could observe multiple sawtooth like peaks of varying spacing. We assigned these peaks as the breaking of ligand-receptor interactions. We use biotin-streptavidin to conform the reliability of the method. The quality and quantity of the SMFS data obtained using this method are much improved. At the end of this chapter, we remeasured dopa-Ti interaction. The rupture force histogram which obtained at a pulling speed of1000nm/s shows the interaction between dopa and Ti is about200pN.In the fourth chapter, we mainly researched on the interaction of dopa-Fe3+. We know that threads from several species exhibit granular cuticles containing a protein that is rich in dopa as well as Fe3+. Granular cuticles exhibit a remarkable combination of high hardness and high extensibility. In the experiment, we found that the rupture force of dopa-Fe3+complex is between250-400pN. It is part of the reason why the byssus cuticles could protect the internal structure.Based on the results shown above, we have known more information about dopa adhesion property, which helps further research of mussel byssus adhesion and design of new functional materials.