Open AccessNatural‐Abundance 13 C Nuclear‐Magnetic‐Resonance Study of Toxin II from Anemonia sulcata
Author(s) -
NORTON Raymond S.,
ZWICK Joachim,
BÉRESS Laszlo
Publication year - 1980
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1980.tb06141.x
Subject(s) - molecule , chemistry , chemical shift , histidine , aspartic acid , stereochemistry , nmr spectra database , ammonium , resonance (particle physics) , nuclear magnetic resonance spectroscopy , carbon 13 nmr , amino acid , spectral line , organic chemistry , biochemistry , physics , particle physics , astronomy
Natural‐abundance 13 C NMR spectra (at 15.04 MH z ) of the polypeptide toxin II from the sea anemone Anemonia sulcata have been analysed and compared with corresponding spectra reported recently for a closely related polypeptide anthopleurin A. The spectra contain many resolved onecarbon and two‐carbon resonances from carbonyl, aromatic and methyl carbons, many of which have been assigned to individual carbons in the molecule on the basis of their chemical shifts, including their pH dependence, and by comparison with the 13 C NMR spectrum of anthopleurin A. Analysis of the effects of pH on the spectrum yields estimates for the p K a values of a number of functional groups in the molecule, as follows: side‐chain carboxylates of the two aspartic acid residues 2 and 3.1; COOH‐terminal carboxylic acid, 3.5; imidazolium moieties of the two histidine residues, 6.7 and 7.6; NH 2 ‐terminal ammonium, 8. The similarity between the p K a values of these functional groups in toxin II and those of corresponding groups in anthopleurin A, together with the close agreement between chemical shifts of conserved curbons, indicates that many local interactions are nearly identical in the two molecules, and thus supports the thesis that their overall conformations in solution are similar. However, the local interactions involving one of the aspartic acid residues are altered in toxin II. Together with other data, this leads to a proposal for the site in these two molecules which is responsible for their cardiac stimulatory activity.