Proteins are 30% α-helices, which, together with β-sheets and loops, self-assemble into specific topological arrangements that make biologically active 3-dimensional structures. The α-helix has another important feature: it is capable of folding autonomously (1). Despite the apparently simpler structure, α-helix formation is governed by the same physical principles as protein folding, and recruits a similar array of interactions for its stabilization, including hydrogen bonds, electrostatics, dipole-dipole, and hydrophobic interactions (2). Furthermore, isolated α-helices display very complex conformational behavior. All of these properties have made the α-helix an excellent test lab for protein-folding research. From such efforts we now understand the factors that determine α-helix stability (3) and the timescales and mechanism of α-helix formation (4). New nanosecond laser-induced temperature-jump techniques can detect the kinetics of individual residues within the α-helix (5), producing exciting data with which to refine our understanding of helix formation. However, what has been missing is a technique to detect the complex motions that should take place in the nanosecond timescale in isolated a-helices. In an article appearing in a recent issue of PNAS, Fierz et al. (6) describe the application of the contact formation ultrafast kinetic technique to monitor nanosecond conformational fluctuations in α-helices at equilibrium conditions. The method promises to directly report on previously unobserved and important conformational processes of already formed α-helical segments, such as motion resulting from helix melting at one end and growth at the other.
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