Conversion of a soluble protein into a potent chaperonein vivo

Abstract

20Protein-folding assistance and aggregation inhibition by cellular factors are largely 21 understood in the context of molecular chaperones. As an alternative and complementary 22 model, we previously proposed that, in general, soluble cellular macromolecules including 23 chaperones with large excluded volume and surface charges exhibit the intrinsic chaperone 24 activity to prevent aggregation of their connected polypeptides, irrespective of the connection 25 types, and thus to aid productive protein folding. As a proof of concept, we here 26 demonstrated that a model soluble protein with an inactive protease domain robustly exerted 27 chaperone activity toward various proteins harboring a short protease-recognition tag of 7 28 residues in Escherichia coli. The chaperone activity of this protein was similar or even 29 superior to that of representative E. coli chaperones in vivo. Furthermore, in vitro refolding 30 experiments confirmed the in vivo results. Our findings revealed that a soluble protein 31 exhibits the intrinsic chaperone activity, which is manifested, upon binding to aggregation-32 prone proteins. This study gives new insights into the ubiquitous chaperoning role of cellular 33 macromolecules in protein-folding assistance and aggregation inhibition underlying the 34 maintenance of protein solubility and proteostasis in vivo. 35 36 3