 | Figure 3
Nature Structural Biology
8, 1042 - 1047 (2001)
Published online: 5 November 2001; | doi:10.1038/nsb723
Engineered metal binding sites map the heterogeneous folding landscape of a coiled coilBryan A. Krantz
& Tobin R. Sosnick | | | | Figure 3. Determining folding models.
Change in folding rates versus changes in stability due to metal binding for a, the N-terminal crosslink; b, C-terminal crosslink; c, dimeric A24G; and d, dimeric A24 . Linear fits, shown with solid lines (a,b) and dotted lines (c,d), are for a homogeneous pathway. Hyperbolic relationships (c,d) represent a heterogeneous model for dimeric GCN4 (Eq. 4). Insets: Relative flux,  f, through the metal-bound pathway is plotted as a function of the change in stability (Eq. 5). Because the crosslinked versions (a,b) have robust homogeneous pathways, their respective f -values are constant. In contrast, the dimeric proteins (c,d) have variable f -values that vary from 0 to 1 according to  and the added stability. Folding energy landscapes are modeled using and f -values with two pathways with either N- or C-terminal helix nucleation. The unfolded ensemble occupies the outer ring. When GCN4-p1' is crosslinked at the N-terminus (a), the surface possesses a smaller barrier in the absence of M2+ for the N-terminal route with respect to the C-terminal route. Upon the addition of M2+, the barrier of the N-terminal route is lowered, and all the pathways continue to nucleate at the N-terminus. When M2+ is added to the C-terminal crosslinked version (b), all the flux nucleates at the C-terminus, because the N-terminal barrier is too large even following 3 kcal mol-1 stabilization. For the dimeric A24G version (c), the N- and C-terminal barriers are nearly equivalent in the absence of metal, and 50% of the ensemble nucleates at either end. But at high concentrations of M2+, the N-terminal, metal-stabilized route dominates. For the A24 dimeric version (d), nucleation principally occurs at the C-terminus in the absence of M2+. High concentrations of M2+ stabilize the N-terminal barrier to a level comparable to the C-terminal barrier, resulting in nucleation occurring equally at both termini. Graphics were created in Mathematica 4.0 (Wolfram Research, Inc.).
|
| | | |  |
|
