Intracellular signalling proteins as 'smart' agents in parallel distributed processes

In eucaryotic organisms, responses to external signals are mediated by a re pertoire of intracellular signalling pathways that ultimately bring about t he activation/inactivation of protein kinases and/or protein phosphatases. Until relatively recently, little thought had been given to the intracellul ar distribution of the components of these signalling pathways. However, ex perimental evidence from a diverse range of organisms indicates that rather than being freely distributed, many of the protein components of signallin g cascades show a significant degree of spatial organisation. Here, we brie fly review the roles of 'anchor', 'scaffold' and 'adaptor' proteins in the organisation and functioning of intracellular signalling pathways. We then consider some of the parallel distributed processing capacities of these ad aptive systems. We focus on signalling proteins-both as individual 'devices ' (agents) and as 'networks' (ecologies) of parallel processes, signalling proteins are described as 'smart thermodynamic machines' which satisfy 'glu ing' (funetorial) roles in the information economy of the cell. This combin es two information-processing views of signalling proteins. Individually, t hey show 'cognitive' capacities and collectively they integrate (cohere) ce llular processes. We exploit these views by drawing comparisons between sig nalling proteins and verbs. This text/dialogical metaphor also helps refine our view of signalling proteins as context-sensitive information processin g agents. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.