Xavier Daura 2 , Alan
نویسندگان
چکیده
30epartment of Biophysical Chemistry, University of Groningen, Nijenborgh 4 9747 AG, Groningen, The Netherlands A principal component analysis has been applied on equilibrium simulations of a p-heptapeptide that shows reversibIe folding in a methanol solution. The analysis shows that the configurational space contains only three dense sub-states. These states of relatively low tree energy correspond to the "native" left-handed helix, a partly helical intermediate, and a hairpin-like structure. The collection of unfolded conformations form a relatively diffuse cloud with little substructure. Intemal hydrogen-bonding energies were found to correlate well with the degree of folding. The native helical structure folds from the N terminus; the transition Erom the major folding intermediate to the native helical structure involves the formation of the two most C-terminal backbone hydrogen bonds. A fourstate Markov model was found to describe transition frequencies between the conformational states within error limits, indicating that memoryeffects are negligible beyond the nanosecond time-scale. The dominant native state fluctuations were found to be very similar to unfolding motions, suggesting that unfolding pathways can be inferred from fluctuations in the native state. The low-dimensional essential subspace, describing 69 % of the collective atomic fluctuations, was found to converge at time-scales of the order of one nanosecond at all temperatures investigated, whereas folding/unfolding takes place at significantly longer time-scales, even above the melting temperature. (Ç) 2001 Academic Press
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تاریخ انتشار 2003