Gramicidin proton transfer

In the second study, the proton diffusion through a polyglycine analog of the gramicidin channel was analyzed [27]. These simulations showed that the diffusion process is very rapid and furthermore, is assisted by the polypeptide backbone. Thus, the latter emerges cis a key factor for rapid proton transfer through the channel. 

In this chapter, we first introduce biological proton transfers and then present the main concepts used in theoretical models. The power of these models is exemplified by studies carried out on relatively simple and experimentally well documented systems a charmel spanning the membrane (gramicidin) a nonredox enzyme (carbonic anhydrase) and a proton pump driven by fight... 

Figure 5.65. The aliphatic region of the TOCSY spectrum of the cyclic decapeptide Gramicidin-S, 5.7. An 80 ms MLEV-17 spin-lock was used, providing complete transfer along the aliphatic sidechains of each residue. Correlations from the a-protons of proline and ornithine are labelled, with those out to the S-protons corresponding to three-step transfers.

Figure 5.67. The time-dependent propagation of magnetisation along a proton spin system as illustrated for the ornithine residue of Gramicidin-S. Traces are extracted from 2D MLEV-17 TOCSY spectra at the amide NH proton shift and show progressive transfer along the sidechain as the mixing time increases.

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