Site-specific post-translational modifications regulate the binding affinity of <i>Conus amadis</i> α-conotoxin Am2005 to Ac-AChBP

acetylcholine-binding protein (Ac-AChBP), a useful model to study nicotinic acetylcholine receptors (nAChRs). Conserved disulfide core of Am2005 with α-conotoxin LvIA, along with the availability of co-crystal structure of α-conotoxin LvIA with Ac-AChBP, prompted the use of computational methods for predicting 3D structure by homology modelling and calculating binding affinity through peptide-protein docking methods. Site-specific PTMs affect the 3D structure by altering local hydrogen-bonding networks, thereby changing the orientation of side chains in 3D space while retaining canonical globular fold with a helical motif. [P2O,P15O,E16γ]Am2161 exhibits a 2-fold higher binding affinity to Ac-AChBP and MD simulations indicates [P2O,P15O,E16γ]Am2161/[P2O,P8O,E16γ]Am2161 have relatively higher hydrogen bonds with Ac-AChBP. Furthermore, peptides with similar binding affinities differed 3-fold in hydrophobicity, as revealed by aggregation score calculations, confirming the role of PTMs in modulating the hydrophobic patch. These studies unravel the significance of site-specific PTMs in fine-tuning the affinity of α-conotoxin Am2005 to its molecular target, which may aid prey capture.