The energetics of T4 lysozyme reveal a hierarchy of conformations

We have used native state exchange to examine the energy landscape of the w ell-characterized protein T4 lysozyme. Although the protein exhibits two-st ate behavior by traditional probes, the energy landscape determined here is much more complex. The average stability of the C-terminal subdomain is si gnificantly higher than that for the N-terminus suggesting at least two reg ions of unfolding. At a more detailed level, there appears to be a broad co ntinuum of stabilities throughout each region. The overall subdomain hierar chy of energies does not mirror data on the folding pathway for this protei n, challenging the relationship between energy landscapes and folding traje ctories.