Spin Labeling of Potassium Channels

Potassium channels are the ion channels most extensively studied by structural techniques. Whereas high-resolution crystal structures have provided key insights into the molecular architecture of these channels, spin labeling studies have helped to unveil the dynamic structural aspects underlying their function. From a practical standpoint, the popularity of spin labeling studies of potassium channels lies in their small size and relative ease of overexpression. The inherent fourfold symmetry of most potassium channels has also greatly facilitated spin labeling studies. This chapter focuses on the overexpression, purification, spin labeling, and subsequent reconstitution of modified potassium channels. It will discuss the general methods used to produce a suitable spin-labeled potassium channel sample and highlight some of the common pitfalls that can occur along the way. At the end of the chapter, we provide detailed methods to produce spin-labeled samples of KcsA and KvAP, the two most commonly studied potassium channels.