ABSTRACT
This book is concerned with the principles of how proteins work: their structure, evolution, oligomerization, binding, dynamics, and so on. It is not helpful to try to describe all the functions that proteins have, or to present a comprehensive list of all the types of structure that there are, not least because a wide range of information is available in books and on the web. However, in Chapters 7 and 8 we are looking at two key functional areas, because these illustrate the ways that proteins behave, and how their structures allow them to achieve their functions. In Chapter 7 we looked at movement and showed that a single protein, the small GTPase, has spawned a large range of systems that make use of that switch to generate motors: complexity and function coming from a fairly simple origin, but branching out in many directions. In this chapter we look at another major functional area, that of signaling, and examine whether the same is true here. That is, are there simple principles that we can identify that make sense of the bewildering complexity that is signaling? We shall see that there are indeed. Signaling is a relatively recent evolutionary need, which means that the embellishments of evolution are strikingly apparent. However, there are rather few basic mechanisms, which develop naturally from the principles that we have seen in earlier chapters. In particular, we shall see that specificity, a key requirement for signaling, arises not from a single strong interaction but from a collection of weak interactions. Evolution has added extra domains and sequences to achieve the specificity needed.
