Protein domains in eukaryotic signal transduction systems

Abstract

Eukaryotic proteins involved in signal transduction processes are frequently characterized by a modular architecture. These modules, also known as functional domains, are able to fold independently from the rest of the molecule. Typically, they also fulfill particular unit functions that can be separated from each other. Eukaryotic cells must respond to a large array of biological stimuli, and evolution has invented a sophisticated signal transduction network consisting of many different components to cope with the situation. Despite that complexity, the analysis of signaling proteins on the level of functional domains reveals a number of recurrent motifs. For most signaling systems, the unit functions of signal generation, signal detection, and signal destruction are carried out by classes of dedicated functional domains. While the similarity within those classes reflects a similar signaling mechanism, the required specificity is either conferred by the subtle differences between the class members or by highly specific targeting domains. Key examples for highly modularized signal transduction systems include protein phosphorylation or ubiquitination, GTPase signaling, and the multiadaptor mechanism of apoptosis signaling.