title: Geometrical Frustration in Interleukin-33 Decouples the Dynamics of the Functional Element from the Folding Transition State Ensemble.
abstract: Interleukin-33 (IL-33) is currently the focus of multiple investigations into targeting pernicious inflammatory disorders. This mediator of inflammation plays a prevalent role in chronic disorders such as asthma, rheumatoid arthritis, and progressive heart disease. In order to better understand the possible link between the folding free energy landscape and functional regions in IL-33, a combined experimental and theoretical approach was applied. IL-33 is a pseudo- symmetrical protein composed of three distinct structural elements that complicate the folding mechanism due to competition for nucleation on the dominant folding route. Trefoil 1 constitutes the majority of the binding interface with the receptor whereas Trefoils 2 and 3 provide the stable scaffold to anchor Trefoil 1. We identified that IL-33 folds with a three-state mechanism, leading to a rollover in the refolding arm of its chevron plots in strongly native conditions. In addition, there is a second slower refolding phase that exhibits the same rollover suggesting similar limitations in folding along parallel routes. Characterization of the intermediate state and the rate limiting steps required for folding suggests that the rollover is attributable to a moving transition state, shifting from a post- to pre-intermediate transition state as you move from strongly native conditions to the midpoint of the transition. On a structural level, we found that initially, all independent Trefoil units fold equally well until a QCA of 0.35 when Trefoil 1 will backtrack in order to allow Trefoils 2 and 3 to fold in the intermediate state, creating a stable scaffold for Trefoil 1 to fold onto during the final folding transition. The formation of this intermediate state and subsequent moving transition state is a result of balancing the difficulty in folding the functionally important Trefoil 1 onto the remainder of the protein. Taken together our results indicate that the functional element of the protein is geometrically frustrated, requiring the more stable elements to fold first, acting as a scaffold for docking of the functional element to allow productive folding to the native state.
authors.affiliation: Department of Chemistry and Biochemistry, University of California at San Diego (UCSD), La Jolla, CA, United States of America.
authors.forename: Kaitlin M
authors.initials: KM
authors.lastname: Fisher
authors.affiliation: Center for Theoretical Biological Physics (CTBP) and Department of Physics, University of California at San Diego (UCSD), La Jolla, CA, United States of America.|Center for Theoretical Biological Physics (CTBP) and Department of Physics and Astronomy, Chemistry and Biochemistry and Cell Biology, Rice University, Houston, TX, United States of America.
authors.forename: Ellinor
authors.initials: E
authors.lastname: Haglund
authors.affiliation: Center for Theoretical Biological Physics (CTBP) and Department of Physics and Astronomy, Chemistry and Biochemistry and Cell Biology, Rice University, Houston, TX, United States of America.
authors.forename: Jeffrey K
authors.initials: JK
authors.lastname: Noel
authors.affiliation: Department of Chemistry and Biochemistry, University of California at San Diego (UCSD), La Jolla, CA, United States of America.
authors.forename: Kendra L
authors.initials: KL
authors.lastname: Hailey
authors.affiliation: Center for Theoretical Biological Physics (CTBP) and Department of Physics and Astronomy, Chemistry and Biochemistry and Cell Biology, Rice University, Houston, TX, United States of America.
authors.forename: José N
authors.initials: JN
authors.lastname: Onuchic
authors.affiliation: Department of Chemistry and Biochemistry, University of California at San Diego (UCSD), La Jolla, CA, United States of America.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Jennings
mesh_terms: D000067596:Interleukin-33 / Q000737:chemistry*; D007700:Kinetics; D056004:Molecular Dynamics Simulation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013816:Thermodynamics
chemical_list: D000067596:Interleukin-33