Project Area D
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Project Area D: Signal Transduction
Project area D deals with modules of signal transduction and resumes a number of topics that already played a role in project areas A-C. These include the energetisation by GTPases 18 and the functional working cycle, which starts on receiving an input. On the other hand, transduction modules are organised differently from the ribosome or the proteasome, which both are stable, compact protein complexes. One reason is certainly that a transducer has to cope with the delivery of external signals. The general requirement of a target, e.g. the capture of a photon or the binding of a diffusible ligand such as a hormone, implies a certain extension to capture the input signal. In the modules that are activated by light (TP D 1-2, 7) the input is received in receptor proteins and thus by an extracellular signal. In other projects, the input is intracellular and chemical – as a rule a diffusible ligand. Submodular functions such as amplification or feedback (level 2 in Fig. 1) are frequently characteristics or even necessary components of cellular signal transmission.