An adaptor protein network that controls general and regulated proteolysis in Bacillus subtilis

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Protein quality control systems are essential to ensure cellular protein homeostasis and monitor the folding and active state of proteins in all cells. These highly conserved systems include chaperone systems but also AAA+ protease complexes such as Hsp100/Clp proteins in bacteria. The ability to rescue and repair functional proteins by chaperones and/or to remove potentially toxic misfolded protein species by degradation could be considered as two branches of the same cellular protein quality control system. Interestingly, the same AAA+ protease systems are concurrently involved in the signal transduction and control of cellular and developmental processes by regulatory proteolysis of e.g. transcription factors. Proteolysis is mediated by dedicated molecular machines, which are formed by ringforming hexameric AAA+ motor proteins, associated with compartmentalized barrel-like peptidases. Examples for such proteolytic complexes are the proteasome in eukaryotic cells or the prokaryotic Hsp100/Clp proteins interacting with ClpP. Often the same proteolytic machines are used in addition for regulatory purposes, e.g. like regulated proteolysis of key transcription factors to control for example developmental processes. We are interested to understand how in prokaryotic cells the important and terminal cellular decision to degrade a protein for distinct and different regulatory or protein quality control reasons is taken. ClpCP of the soil bacterium Bacillus subtilis is involved in general protein quality control and regulatory processes. We could demonstrate for ClpCP that adaptor proteins like MecA, YpbH or McsB are necessary to activate the ClpCP protease and important for substrate recognition and selection. Based on our recent results we propose to address two interesting and new aspects of this system in more detail. (1) We want to investigate and possibly understand the interplay between the unfolding or remodeling and proteolytic mode of the Hsp100/Clp proteins both in vivo and in vitro. (2) We want to investigate the role and function of the adaptor protein mediated ClpC activation with a special emphasis on the protein arginine kinase McsB. We will test our hypothesis concerning the potential role of McsB in protein disaggregation using various in vivo and in vitro experiments.