| Study of the unfolded states of proteins lends insight into the protein folding problem. A well-studied system, the unfolded state of the N-terminal drk SH3 domain, has been structurally characterized using NMR spectroscopy and other techniques. The computer program ENSEMBLE (Choy and Forman-Kay, 2001) can model the rapidly-interconverting unfolded state ensemble, based on this experimental data. To extend the constraint types usable by ENSEMBLE, the distance-dependent paramagnetic relaxation enhancement (PRE) was measured on a modified SH3 domain; a small ATCUN motif was added to the domain, which binds a paramagnetic Cu2+ ion. Models that predict the position of the copper atom fit well to the experimental PRE data, and an ENSEMBLE restraint based on PRE values was compatible with other structural information. These results support the utility of ATCUN-derived PRE data for characterization of unfolded states, an important goal in understanding protein structure, stability, and function. |
