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Popova, Kristina (2014): GroEL/ES modulates the mechanism and accelerates the rate of TIM-barrel domain folding. Dissertation, LMU München: Fakultät für Chemie und Pharmazie



The interactome of GroEL/ES has been characterized extensively in several studies and substrates of the chaperonin have been classified (Kerner et al., 2005; Fijiwara et al., 2010). However, the question of what makes some proteins GroEL-dependent and how exactly the chaperonin system promotes their folding remained unresolved. Moreover, it has been unclear how the chaperonin acts on its substrates and whether the protein folding pathway is modified inside the cage as compared to free solution. The aim of this study, therefore, was to characterise and compare the spontaneous and chaperonin-assisted refolding pathway of an obligate substrate of GroEL/ES, in order to elucidate the mechanism of GroEL/ES action. This study presents evidence that encapsulation in the GroEL/ES-cage accelerates the rate and modulates the mechanism of folding of its obligate TIM-barrel substrate, dihydrodipicolinate synthase. We found that the spontaneous refolding of DAPA is slow due to high cooperativity of the process, as it initiates from an ensemble of unstructured intermediates. We demonstrated that the confining environment of the chaperonin cage promotes formation of the TIM-barrel structure in a segmental manner, lowering the entropic component of the activation barrier and accelerating the rate of DAPA folding. Moreover, the spontaneous refolding pathway of a GroEL-independent homolog of DAPA, MsNANA, closely resembles that of DAPA inside the chaperonin cage. Thus, we conclude that GroEL/ES is a powerful folding catalyst for the substrates that otherwise fail to effectively reach their native state.