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Transition State Heterogeneity in GCN4 Coiled Coil Folding Studied by Using Multisite Mutations and Crosslinking
Liam B. Moran, Joel P. Schneider, Alex Kentsis, Giridher A. Reddy and Tobin R. Sosnick
Proceedings of the National Academy of Sciences of the United States of America
Vol. 96, No. 19 (Sep. 14, 1999), pp. 10699-10704
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/48816
Page Count: 6
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We have investigated the folding behavior of dimeric and covalently crosslinked versions of the 33-residue α -helical GCN4-p1 coiled coil derived from the leucine zipper region of the transcriptional activator GCN4. The effects of multisite substitutions indicate that folding occurs along multiple routes with nucleation sites located throughout the protein. The similarity in activation energies of the different routes together with an analysis of intrinsic helical propensities indicate that minimal helix is present before a productive collision of the two chains. However, approximately one-third to one-half of the total helical structure is formed in the postcollision transition state ensemble. For the crosslinked, monomeric version, folding occurs along a single robust pathway. Here, the region nearest the crosslink, with the least helical propensity, is structured in the transition state whereas the region farthest from the fether, with the most propensity, is completely unstructured. Hence, the existence of transition state heterogeneity and the selection of folding routes critically depend on chain topology.
Proceedings of the National Academy of Sciences of the United States of America © 1999 National Academy of Sciences