Effect of linker length on avidin binding to biotinylated gramicidin A

by Anastasiadis, A.; Morton, C. J.; Talbo, G. H.; Koeppe, R. E.; Separovic, F.

Biotinylated gramicidins are an important component of the AMBRI (R) "ion channel switch (TM)" biosensor. These gramicidin A (gA) analogues have a biotin attached to the C-terminus of gA Via a number of aminocaproyl linker groups (X). The Structure of gA5XB has been determined in deuterated sodium dodecyl Sulfate micelles and is similar to native gA and other modified gA analogues. The biotin and aminocaproyl groups were mobile and located in the aqueous phase and when avidin was added, NMR and MS Studies showed that gA5XB bound more effectively to avidin than gA2XB. The length and flexibility of the linker appears to be important for biotin-avidin binding and, in the AMBRI (R) biosensor, gA5XB is I more effective gated ion channel than gA2XB. The conformation and dynamics of the aminocaproyl linker groups were investigated using H-2 solid-state NMR. Deuterated aminocaproyl linkers were Coupled to gA and incorporated into oriented bilayers in order to analyse the order and dynamics of the aminocaproyl linker. The small H-2 splittings and the T-1 relaxation times indicated that the aminocaproyl linker is undergoing fast rotation in phospholipid bilayers. Native d(4)-gA as well as d(4)-gA2XB, where the ethanolamine has been deuterated, were also incorporated into oriented bilayers. Solid-state H-2 NMR data showed that the addition of the linker group restricted the mobility of the ethanolamine. However, these modifications to the C-terminus of gA did not interfere with ion channel function and clarify how the biotinylated gA analogues perform in the lipid bilayer as part of the AMBRI (R) biosensor.

International Journal of Peptide Research and Therapeutics
Start Page
1573-3904; 1573-3149