| Summary: | The 270-MHz proton NMR spectra of the unique long neurotoxins bearing Phe-25, Astrotia stokesii b (As b) and Astrotia stokesii c (As c) from Astrotia stokesii , and Acanthophis antarcticus b (Aa b) from Acanthophis antarcticus , have been analyzed. The aromatic proton resonances of Phe-25 in As b and Aa b were assigned on the basis of the nuclear Overhauser effects observed on irradiation of slowly exchanging amide protons. Phe-25 was found to be involved in hydrophobic interactions with Ile/Val-42, Ala-46 and Ile-58 in As b and As c, and with Ala-46 and Val-58 in Aa b. These hydrophobic interactions, instead of the hydrogen bond between Tyr-25 and Glu-42 found in other neurotoxins, appear to be important for maintenance of the biologically active tertiary structure. The pH dependency of the chemical shift and intensity of the Trp-72 N-l proton resonance of As b indicates that the indole ring is not fully exposed to the solvent and that the extra tail segment of this long neurotoxin interacts with the main part of the molecule.
|
|---|