TITLE: "Dynamics of the primary processes of protein folding: Helix nucleation"

SPEAKER: Dr. Jamers Werner,

TIME: Thursday Feb. 1, 2001 at 4 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

While the transition from a random coil of amino acids to an alpha helix conformation is arguably one of the best understood kinetic processes in the field of protein folding, certain aspects of the helix/coil transition remain in question. In particular, the time-scale on which a section of residues in a completely random coil conformation folds into a stable run of alpha-helical residues (helix nucleation) has been reported to vary from several nanoseconds to several milliseconds. This enormous range of reported rates makes it unclear whether helix nucleation is a very early process that facilitates subsequent folding events, or whether it is a rate limiting late step in folding. The current studies directly examine alpha-helix nucleation kinetics from opposite sides of the helix/coil transition. Rapid, laser-induced temperature jumps (T-jumps) were used to perturb the helix/coil equilibrium and time resolved infrared absorption of the amide I band was used to report on the peptide conformation. The results show helix nucleation to occur on a sub-microsecond time-scale with a substantial enthalpic barrier.