The bottom-up design of protein-based signaling networks is a key goal of synthetic biology – yet, it remains elusive due to our inability to tailor-make signal transducers and receptors that can be readily compiled into defined signaling motifs and networks. Towards this goal, we report a generic approach for the construction of protein-based molecular switches based on artificially autoinhibited proteases. Using a combination of structure-guided design, directed evolution and molecular plug-and-play, we created a set of protease-based molecular switches derived from Tobacco Vein Mottling Virus (TVMV) and Hepatitis C Virus (HCV) that can sense different molecular queues and translate them into a defined proteolytic signal. These include protease-based biosensors have been developed that can sense clinically important proteases in a highly specific and sensitive manner, protease-based proximity sensors that can detect protein-protein interactions and allosterically regulated protease receptors that can respond to defined peptide ligands in switch-ON and switch-OFF fashions. We also demonstrate how different types of protease-based ligand receptors and signal transducers can be assembled into integrated signal sensing and amplification circuits with >30-130-fold signal amplification. Overall, we anticipate this signaling platform to find widespread applications in molecular diagnostics, and will also allow us to probe the fundamental principles that underlie biomolecular signaling events using defined components in vitro and in live cells that, at least in principle, can be connected to any biological process.