Several model systems have been used to evaluate the alpha-helical propensities of different amino acids. In contrast, experimental quantitation of beta-sheet preferences has been addressed in only one model system, a zinc-finger peptide. Here we measure the relative propensity for beta-sheet formation of the twenty naturally occurring amino acids in a variant of the small, monomeric, beta-sheet-rich, IgG-binding domain from protein G. Amino-acid substitutions were made at a guest site on the solvent-exposed surface of the beta-sheet. Several criteria were used to establish that the mutations did not cause significant structural changes: binding to the Fc domain of IgG, calorimetric unfolding and NMR spectroscopy. Characterization of the terminal stabilities of these proteins leads to a thermodynamic scale for beta-sheet propensities that spans a range of approximately 2 kcal mol-1 for the naturally occurring amino acids, excluding proline. The magnitude of the differences suggests that beta-sheet preferences can be important determinants of protein stability.
Submitter: Marie Ary
Submission Date: July 31, 2017, 11:46 a.m.
|Number of data points||80|
|Assays/Quantities/Protocols||Experimental Assay: ΔΔG (321K) ; Experimental Assay: Tm ; Experimental Assay: Ka/Ka(AASS-53Thr) IgG-Fc|
|Libraries||Substitution of all 20 aa at position 53 in host environment (Gβ1 M1T + I6A;T44A;T51S;T55S) (Table 1)|