Abstract
Ubiquitin-like modifications regulate nearly every aspect of cellular functions. A key step in these modifications is the recognition of the carrier enzyme (E2) by the activating enzyme (E1). In this study, we have found that a critical E2-binding surface on the E1 of the small ubiquitin-like modifier has unusually high populations in both ordered and disordered states. Upon binding the E2, the disordered state is converted to the ordered state, which resembles the structure of the bound conformation, providing a mechanism to resolve the "Levinthal Paradox" search problem in a folding-upon-binding process. The significance of the folding-unfolding equilibrium is shown by the loss of functions of the mutations that shift the equilibrium to the folded state. This study highlights the importance of conformational flexibility in the molecular recognition event.
Highlights
The conjugation of ubiquitin or ubiquitin-like proteins to other cellular proteins is one of the most important mechanisms in regulating cellular functions in eukaryotic systems and is broadly involved in controlling the life spans, trafficking, and functions of a wide range of proteins [1,2,3,4]
We have found that a critical E2-binding surface on the E1 of the small ubiquitin-like modifier has unusually high populations in both ordered and disordered states
E1 catalyzes the adenylation of the C-terminal carboxyl group of the ubiquitin-like protein (Ublp), and it forms a thioester bond between the –SH group of the active site Cys residue and the C-terminal carboxyl group of the Ublp
Summary
The conjugation of ubiquitin or ubiquitin-like proteins to other cellular proteins is one of the most important mechanisms in regulating cellular functions in eukaryotic systems and is broadly involved in controlling the life spans, trafficking, and functions of a wide range of proteins [1,2,3,4]. Using specially designed mutations to shift the conformational equilibrium to the ordered state but not altering the structure at the binding surface, we have shown that the folding-unfolding equilibrium in the E1 Ubl domain is important for the recognition of E2 in SUMO conjugation.
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