Henry Rzepa's Blog Chemistry with a twist

April 9, 2011

Why are α-helices in proteins mostly right handed?

Understanding why and how proteins fold continues to be a grand challenge in science. I have described how Wrinch in 1936 made a bold proposal for the mechanism, which however flew in the face of much of then known chemistry. Linus Pauling took most of the credit (and a Nobel prize) when in a famous paper[1] in 1951 he suggested a mechanism that involved (inter alia) the formation of what he termed α-helices. Jack Dunitz in 2001[2] wrote a must-read article[3] on the topic of “Pauling’s Left-handed α-helix” (it is now known to be right handed). I thought I would revisit this famous example with a calculation of my own and here I have used the ωB97XD/6-311G(d,p) DFT procedure[4] to calculate some of the energy components of a small helix comprising (ala)6 in both left and right handed form.

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References

  1. L. Pauling, R.B. Corey, and H.R. Branson, "The structure of proteins: Two hydrogen-bonded helical configurations of the polypeptide chain", Proceedings of the National Academy of Sciences, vol. 37, pp. 205-211, 1951. http://dx.doi.org/10.1073/pnas.37.4.205
  2. J.D. Dunitz, "Pauling's Left-Handed α-Helix", Angewandte Chemie International Edition, vol. 40, pp. 4167-4173, 2001. http://dx.doi.org/10.1002/1521-3773(20011119)40:22<4167::AID-ANIE4167>3.0.CO;2-Q
  3. K.S. Thanthiriwatte, E.G. Hohenstein, L.A. Burns, and C.D. Sherrill, "Assessment of the Performance of DFT and DFT-D Methods for Describing Distance Dependence of Hydrogen-Bonded Interactions", Journal of Chemical Theory and Computation, vol. 7, pp. 88-96, 2010. http://dx.doi.org/10.1021/ct100469b

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