The Structure and Function Relationship between Guangxitoxin and the Voltage-Gated Potassium Channel Kv2.

Proteins are the functional units of biology. They are essential in physiological processes. To achieve their functions, each protein folds into a characteristic three dimensional structure encoded by its primary amino acid sequence. Voltage-gated ion channels (VGICs) are a well-studied class of proteins which form pores in membranes permitting the conduction of ions. Voltage-gated potassium (Kv) channels are a specific subtype of VGICs in which the functional protein is tetrameric with each monomer consisting of six transmembrane (S1-S6) helices. Kv channels are all selective for potassium ions, yet are composed of many different subtypes which show sequence diversity and variation in cellular expression. With such diversity, their physiological contribution is difficult to determine without selective inhibitors of specific ion channel subtypes. Fortunately, natural sources of ion channel inhibitors have been found in venoms of animals such as tarantulas and scorpions. In this work I focused on the Kv2.1 channel and its interaction with the tarantula venom peptide Guangxitoxin (GxTX).;In the subsequent chapters it will first introduce the physiological context of Kv2.1 activity. Functionally, Kv2.1 belongs to the delayed rectifier class of Kv channels showing sigmoidal activation in response to voltage and slow inactivation. Secondly; I will present electrophysiological measurements and chemical modification of GxTX to show the functional state of Kv2.1 modulates toxin affinity and binding kinetics. Thirdly, I will present a study using homology modeling to develop structural hypotheses of complexes of GxTX binding to the channel. Lastly, I will propose a functional mechanism for how Kv2.1 activity is modulated when GxTX is bound.