Interest in the unfolded state of proteins has grown with the realization that this state can have considerable structure in the absence of denaturants. Natively unfolded proteins, mutations that unfold proteins under native conditions, and changes in pH that induce unfolding are attractive models for the unfolded state in the absence of denaturant. The unfolded state of the N-terminal domain of ribosomal protein L9 (NTL9) was previously shown to contain significant non-native electrostatic interactions [Cho, J. H., Sato, S., and Raleigh, D. P. (2004) J. Mol. Biol. 338, 827-837]. NTL9 has a mixed alpha-beta structure and folds via a two-state mechanism. We have generated a model of the unfolded state of NTL9 in the absence of denaturant by substitution of an alanine for phenylalanine 5 located in the core of this protein. The CD spectrum of the variant, denoted as F5A, exhibits significantly less structure than the wild type; however, the mean residue ellipticity of F5A at 222 nm (-8200 deg cm(2) dmol(-)(1)) is considerably larger than expected for a fully unfolded protein, indicating that residual secondary structure is populated. F5A also has more residual structure than the urea-unfolded wild type. The stability of F5A is estimated to be at least 1 kcal/mol unfavorable, showing that the unfolded state is populated to 84% or more. NMR pulsed-field gradient measurements yield a hydrodynamic radius of 16.1 A for wild-type NTL9 and 20.8 A for the F5A variant in native buffer. The physiologically relevant unfolded state of wild-type NTL9 is likely to be even more compact than F5A since the mutation should reduce the level of hydrophobic clustering in the unfolded state in the absence of denaturant. The hydrodynamic radius of F5A increases to 25.9 A in 8 M urea, and a value of 23.5 A is obtained for the wild type under similar conditions. The results show that the unfolded state of F5A in the absence of denaturant is more compact and contains more structure than the urea-unfolded form. Study holds ProTherm entries: 20158, 20159, 20160, 20161, 20162, 20163, 20164 Extra Details: electrostatic interactions, stability, ribosomal protein L9, hydrophobic clustering.
Submitter: Connie Wang
Submission Date: April 24, 2018, 8:52 p.m.
|Number of data points||17|
|Proteins||50S ribosomal protein L9 ; 50S ribosomal protein L9|
|Assays/Quantities/Protocols||Experimental Assay: m details:Additives TMOA (Trimethylamine N-oxide) (3 mM), ; Experimental Assay: dG_H2O details:Additives TMOA (Trimethylamine N-oxide) (3 mM), ; Experimental Assay: m details:Additives ; Experimental Assay: dG_H2O details:Additives ; Derived Quantity: ddG_H2O details:Additives TMOA (Trimethylamine N-oxide) (3 mM), ; Derived Quantity: ddG_H2O details:Additives|
|Libraries||Mutations for sequence MKVIFLKDVKGKGKKGEIKNVADGYANNFLFKQGLAIEATPANLKALEAQKQKEQRQAAEELANAKKLKEQLEKLTVTIPAKAGEGGRLFGSITSKQIAESLQAQHGLKLDKRKIELADAIRALGYTNVPVKLHPEVTATLKVHVTEQK|