Caulobacter crescentus folding machines at the interface of inheritance, cell division, and energy metabolism

Abstract: All living cells must perform essential biological processes while monitoring and responding to environmental cues. Bacteria are accessible experimental systems in which to study the function of conserved central processes. One of the most highly conserved systems between different organisms is the proteostasis network; a group of chaperones and proteases that work collectively to repair and remove damaged proteins that accumulate in living systems. In the work of this thesis, we investigate how folding machines of the proteostasis network are integrated with central biological processes in the model organism Caulobacter crescentus, and examine how these relationships change during stress.Asymmetrically-dividing C. crescentus has previously been described to undergo aging, with the accumulation of protein aggregates in the larger stalked cell proposed to drive replicative decline in this organism. In study I, we establish C. crescentus as a model for monitoring the dynamic cellular response to protein aggregation. Using this system, we demonstrate that protein aggregates are shared during division, and do not preferentially collect in one cell type.The ubiquitous GroESL folding machine, which provides a specialized environment for folding specific proteins, has been previously linked to the C. crescentus cell cycle through an unknown mechanism. In study II, we discover that GroESL folding is required to support division both in optimal conditions and during mild stress. Specifically, we find that GroESL supports the function of proteins that interact with the highly conserved bacterial division scaffold FtsZ, as well as proteins that direct synthesis of the peptidoglycan cell envelope layer.In study III we investigate the functional link between GroESL folding and energy metabolism, and find that the chaperonin has a conserved role in folding respiratory and metabolic proteins, thereby supporting the central pathways these proteins function in. Furthermore, we find that GroESL protects several of these proteins from aggregation during stress.Taken together, the work of this thesis addresses current models of prokaryotic damage segregation and aging, expands on how chaperonin folding is integrated into the essential process of division, and demonstrates a functional role for protein folding in protecting energy metabolism during stress. The findings of this research thereby provide novel insight into how fundamental biological processes interface with protein folding machines.