Hydroxyproline-induced Helical Disruption in Conantokin Rl-B Affects Subunit-selective Antagonistic Activities toward Ion Channels of N-Methyl-D-aspartate Receptors

作者：Kunda Shailaja; Yuan Yue; Balsara Rashna D; Zajicek Jaroslav; Castellino Francis J^*

来源：JOURNAL OF BIOLOGICAL CHEMISTRY, 2015, 290(29): 18156-18172.

DOI：10.1074/jbc.M115.650341

Conantokins are similar to 20-amino acid peptides present in predatory marine snail venoms that function as allosteric antagonists of ion channels of the N-methyl-D-aspartate receptor (NMDAR). These peptides possess a high percentage of post-/co-translationally modified amino acids, particularly gamma-carboxyglutamate (Gla). Appropriately spaced Gla residues allow binding of functional divalent cations, which induces end-to-end alpha-helices in many conantokins. A smaller number of these peptides additionally contain 4-hydroxyproline (Hyp). Hyp should prevent adoption of the metal ion-induced full alpha-helix, with unknown functional consequences. To address this disparity, as well as the role of Hyp in conantokins, we have solved the high resolution three-dimensional solution structure of a Gla/Hyp-containing 18-residue conantokin, conRl-B, by high field NMR spectroscopy. We show that Hyp(10) disrupts only a small region of the alpha-helix of the Mn(2+.)peptide complex, which displays cation-induced alpha-helices on each terminus of the peptide. The function of conRl-B was examined by measuring its inhibition of NMDA/Gly-mediated current through NMDAR ion channels in mouse cortical neurons. The conRl-B displays high inhibitory selectivity for subclasses of NMDARs that contain the functionally important GluN2B subunit. Replacement of Hyp10 with N(8)Q results in a Mg2+-complexed end-to-end alpha-helix, accompanied by attenuation of NMDAR inhibitory activity. However, replacement of Hyp(10) with Pro(10) allowed the resulting peptide to retain its inhibitory property but diminished its GluN2B specificity. Thus, these modified amino acids, in specific peptide backbones, play critical roles in their subunit-selective inhibition of NMDAR ion channels, a finding that can be employed to design NMDAR antagonists that function at ion channels of distinct NMDAR subclasses.

• 出版日期2015-7-17