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The Helical Alanine Controversy:  An (Ala)6 Insertion Dramatically Increases Helicity

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journal contribution
posted on 27.10.2004 by Jasper C. Lin, Bipasha Barua, Niels H. Andersen
Employing chemical shift melts and hydrogen/deuterium exchange NMR techniques, we have determined the stabilization of the Trp-cage miniprotein due to multiple alanine insertions within the N-terminal α-helix. Alanine is shown to be uniquely helix-stabilizing and this stabilization is reflected in the global fold stability of the Trp-cage. The associated free energy change per alanine can be utilized to calculate the alanine propagation value. From the Lifson−Roig formulation, the calculated value (wAla = 1.6) is comparable to those obtained for short, solubilized, alanine-rich helices and is much larger than the values obtained by prior host−guest techniques or in N-terminally templated helices and peptides bearing long contiguous strings of alanines with no capping or solubilizing units present.

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