Diversity And Structures Of Ion Channels

Abstract

We are now ready to explore the vast variety and diversity of voltage-sensitive ion channels. While this book is primarily devoted to a study in depth of the way in which these channels carry out their functions, this chapter is devoted to a broad review of voltage-sensitive ion channels in living organisms. To deal with such a vast and growing array of data it has become necessary develop classifications of ion channels into families. The most important of these are based on the organic evolution of these protein molecules. When studying emergent phenomena in complex systems, the reductionist approach of looking at smaller and smaller components is not enough. We must remain aware of the important information we gathered at larger scales, both in the time domain and in the frequency domain. While we have been looking at voltage-sensitive ion channels as an intellectual challenge, a problem to be solved, these channels are crucial components of our lives. When channels mutate, they sometimes cause diseases, and we will briefly discuss these for each type of channel. Ion channels occur in all biological kingdoms. In plants, the photoreceptor phytochrome is involved in flowering, seed germination and other plant responses by controlling transcription of many light-activated genes dealing with chloroplast development. The 124-kDa phytochrome protein contains a chromophore that responds to light by controlling the influx of Ca 2+ into the cell. 1 Fungal and bacterial channels are discussed in the last two sections. The rest of the chapter will focus on voltage-sensitive ion channels found in the animal kingdom. 1. THE ROLE OF STRUCTURE Although it would be of great value to learn the detailed structure of every channel of interest, we should not expect the knowledge of the structure by itself to tell us how the channel works. Would a person who did not know about ferromagnetism or the Earth's magnetic field understand how a compass works by taking it apart? Clearly, structural information is only part of the picture; we need a theory as well. But structure is an important part of the picture: We cannot understand channels without knowing their structure.