In contrast, none of the control peptides were able to compete with [125I]α-BTX for binding to the α7-nAChR (Fig. 2D).
The modulation observed here, of choline binding to the α7-nAChR by T30, suggests another potential functional justification for the presence of AChE in tissues devoid of its familiar substrate.
In any event, these results demonstrate that a 30mer peptide, and to a lesser extent one of its 14mer derivatives, define a domain within the C-terminus of AChE that has the capacity for selective interaction with the α7-nAChR, not only binding to the α7-nAChR and altering its affinity for endogenous agonists, but also upregulating expression of the receptor itself.
The observation that T30 can alter choline binding to the α7-nAChR, is of particular interest, since choline can act as the primary endogenous ligand for the α7-nAChR during development of the nervous system [74] and in areas of the mature brain, where, paradoxically, both AChE and the α7-nAChR are highly expressed [48] [49], but there is little or no acetylcholine [24].
In contrast to the effects seen for T14 and T30, the control peptides S14, T15, B14 and SB14 had no effect on [125I]α-BTX binding to the α7-nAChR, thus demonstrating the specificity of T14 and T30 peptides at this receptor.
In contrast, the binding to the α3β2 nAChR subtype is likely to be similar to that observed in our AChBP/conotoxin complex, including an important contribution to binding from the Arg5-Asp195 salt bridge.
This study provides evidence that two peptides derived from the C-terminus of acetylcholinesterase, not only selectively displace specific bungarotoxin binding at the α7-nAChR, but also alter receptor binding properties for its familiar ligands, including the alternative endogenous agonist choline.
In contrast, A-844606 exhibited negligible displacement of [3H]cytisine binding to α4β2 nAChRs (IC50>30,000 nM) [27].
In contrast to results obtained with the peptides alone, co-application of T30 with ACh, MLA, or choline altered binding of these ligands to the α7-nAChR.
Preliminary screening of the binding of both peptides to the α7-nAChR, when compared with that of acknowledged receptor agonists and antagonists, revealed significant, but incomplete, competition with [125I]α-BTX for receptor binding sites (Fig. 2C).
