TIME RESOLVED STUDIES OF HELIX COIL TRANSITION IN SMALL PEPTIDES

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Alpha-helix is a common structural motif in proteins. Understanding its folding mechanism is therefore important for understanding how large proteins fold. The helix-coil transition has been studied extensively in the past, including recent theoretical and experimental efforts as well as studies involving laser-induced T-jump methods. Although a detailed mechanism of the helix-coil transition has begun to emerge, controversy still exists. In this work we are going to study the helix-coil transition in a synthetic 19 residue Ala-based helical peptide using laser-induced T-jump for rapid refolding/unfolding initiation and time-resolved infrared spectroscopy for relaxation measurements. Experimental results will be compared to theoretical model predictions. It is well-known that end caps and the peptide length can dramatically influence the thermodynamics of the helix-coil transition. However, their roles in determining the kinetics of the helix-coil transition have not been studied extensively and are less well understood. Kinetic Ising models and sequential kinetic models involving barrier crossing via diffusion all predict that the helix formation time depends monotonically on the peptide length with the relaxation time increasing with respect to increasing chain length. Here, we have studied the helix-coil transition kinetics of a series of Ala-based alpha-helical peptides of different length (19-39 residues), with and without end caps, using time-resolved infrared spectroscopy coupled with laser-induced temperature jump (T-jump) initiation method.