Abstract
Poly(glutamic acid) has been studied with a nanosecond T-jump experiment. A new experimental set-up based on the frequency-quadrupling of an 82 MHz Titanium-Sapphire laser allows rapid CD measurements to be performed. Combining time-resolved absorption and circular dichroism at 204 and 220 nm, we are able to measure precisely the unfolding relaxation time as well as the helical fraction evolution. We show that only CD at 220 nm is relevant to observe the unfolding of an alpha helix whereas no change is observed for CD at 204 nm. Conversely, both absorptions yield information on the dynamics of the process.
Highlights
Protein folding remains one of the most important challenges in modern biophysics [1]
We have carried out measurement of the steady-state absorption and circular dichroism (CD) spectra of the poly(glutamic acid) (PGA)
Thanks to CD measurements, we can ascertain that we observe an unfolding of the alpha helices in PGA following the 4 °C T-jump
Summary
Protein folding remains one of the most important challenges in modern biophysics [1]. The mechanisms by which an unfolded protein finds its way to its unique native conformation are still largely under debate. Even though the overall phenomena are quite well understood, in particular with the existence of some funnel energy surface which guides the protein towards its final state [2], the microscopic details are not so well-known. It has become clear that formation of secondary structures (alpha helices, beta strands) often plays a determinant role as a first step in this folding pathway, creating some kinds of nucleation centers from which the folding propagates.
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