Intracellular signalling proteins as `smart agents in parallel distributed processes

In eucaryotic organisms, responses to external signals are mediated by a repertoire of intracellular signalling pathways that ultimately bring about the activation/inactivation of protein kinases and/or protein phosphatases. Until relatively recently, little thought had been given to the intracellular distribution of the components of these signalling pathways. However, experimental evidence from a diverse range of organisms indicates that rather than being freely distributed, many of the protein components of signalling cascades show a significant degree of spatial organisation. Here, we briefly review the roles of `anchorʹ, `scaffoldʹ and `adaptorʹ proteins in the organisation and functioning of intracellular signalling pathways. We then consider some of the parallel distributed processing capacities of these adaptive systems. We focus on signalling proteins-both as individual `devicesʹ (agents) and as `networksʹ (ecologies) of parallel processes. Signalling proteins are described as `smart thermodynamic machinesʹ which satisfy `gluingʹ (functorial) roles in the information economy of the cell. This combines two information-processing views of signalling proteins. Individually, they show `cognitiveʹ capacities and collectively they integrate (cohere) cellular processes. We exploit these views by drawing comparisons between signalling proteins and verbs. This text/dialogical metaphor also helps refine our view of signalling proteins as context-sensitive information processing agents.