Peptide nanotubes gramicidin

Two molecules of the ion-channel-forming peptide gramicidin, which contains alternating L- and D-amino acids, have been shown to form a membrane-spanning P-helix. The alternation of L- and D-amino acids is a feature of a series of cyclic peptides that self-assemble into membrane spanning nanotubes. P-Helices have now also been shown to occur as a structural element in proteins consisting only of L-a-amino acids, viz. in the enzyme pectate lyase. Related to the naturally... 

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