A versatile method to measure the binding to basic proteins by surface plasmon resonance

Biomolecular interaction is a fundamental mechanism involved in many critical biological processes including gene transcription, translation, and cell signaling networks. Many basic proteins, such as histones, transcription factors, and ribosomal proteins, participate in the interaction of these processes. Surface plasmon resonance (SPR) has been used as a “gold” standard to measure biomolecular interactions. One key issue in SPR assay is how to immobilize ligand without affecting its conformation and biological activity. In this study, we developed a novel method for measuring bindings to basic proteins by SPR, wherein the naturally positive charge of basic protein was utilized to immobilize ligand. The electrostatic interaction between the basic proteins and the negatively charged C1 chip surface (Biacore, GE) generated a specific and stable immobilization without any modification; sodium dodecyl sulfate was identified to be efficient enough for the complete regeneration that allows fresh ligand to be immobilized in each cycle for an optimal kinetic assay. With those parameters determined, an efficient, fast, and reversible method was established to measure bindings to basic proteins under physiological conditions. This new method is widely applicable to the study of binding kinetics between protein-, DNA-, or RNA- and basic protein.