Metal-Binding Properties of Conus Parius Conantokin Variants and Their Inhibitory Effect on the NMDA Receptor

Little is known of the structure and function of conantokins from the species Conus parius. Their surprising deviation from what was previously considered to be the conantokins consensus sequence allowed in this study for the exploration of how posttranslational modifications of the toxin region affect the characteristic helical structure and, subsequently, the requisite inhibitory effect upon the N-methyl-D-aspartate (NMDA) receptor. Synthesized variants of the wild-type conantokin Conus Parius 2 were tested by isothermal titration calorimetry, circular dichroism, and electrophysiology experiments to explore the variation's effect on structure and function. Variations included mutated gamma-carboxyglutamate residues (Gla) in position 4, 7, and 11, 4-trans-hydroxyproline in position 3, and an amidation at the N-terminus, a modification found in all non-Conus parius conantokins. It was found that Gla in positions 4 and 7, and hydroxyproline were most critical for the retention of helicity and inhibition potential towards the NMDA receptor.