NMR structure of C-terminally tagged gramicidin channels

A biotin group was covalently attached to the C terminus of gramicidin A (g A) through a linker arm comprising a glycine residue with either one (gAXB) or two caproyl groups (gAXXB). High-resolution two-dimensional NMR spectro scopy was used to determine the structure of these modified gA analogues an d [Lys(16)]gramicidin A (gA-Lys) in sodium dodecyl-d(25) sulphate micelles. Gated gA ion channels based on linking a receptor group to these gA analog ues have been used recently as a component in a sensing device. The conform ations of the gA backbones and amino acid side chains of lysinated gA and b iotinylated gA in detergent micelles were found to be almost identical to t hat of native gA, i.e. that of an N-terminal to N-terminal (head to head) d imer formed by two right-handed, single-stranded beta(6.3) helices. The bio tin tail of the gAXB and gAXXB and the lysine extremity of gA-Lys appeared to lie outside the micelle. Thus it appears that the covalent attachment of functional groups to the C terminus of gA does not disrupt the peptide's h elical configuration. Further, single channel measurements of all three gA analogues showed that functioning ion channels were preserved within a memb rane environment. (C) 1999 Elsevier Science B.V. All rights reserved.