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Protolytic properties of polyamine wasp toxin analogues studied by 13C NMR spectroscopy

✍ Scribed by Kristian Strømgaard; Lorna Piazzi; Christian A. Olsen; Henrik Franzyk; Jerzy W. Jaroszewski

Publisher
John Wiley and Sons
Year
2006
Tongue
English
Weight
453 KB
Volume
44
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

Acid–base properties of the natural polyamine wasp toxin PhTX‐433 (1) and seven synthetic analogues [PhTX‐343 (2), PhTX‐334 (3), PhTX‐443 (4), PhTX‐434 (5), PhTX‐344 (6), PhTX‐444 (7), and PhTX‐333 (8)], each having four protolytic sites, were characterized by ^13^C NMR spectroscopy. Nonlinear, multiparameter, simultaneous fit of all chemical shift data obtained from the NMR titration curves yielded macroscopic p__K__~a~ values as well as intrinsic chemical shift data of all differently protonated macrospecies. Analyses of the chemical shift data demonstrated strong interactions between all four sites and provided information about complex relationships between chemical shift values and protonation state. Deprotonation of fully protonated forms starts at the central amino group of the polyamine moiety, and the extent of this trend depends on the distance to the flanking, protonated amino groups. The p__K__~a1~ values of 1–8 are in the range 8.2–9.4. Hence, some of the toxins are incompletely protonated at the pH and ionic strength conditions used for assessment of their interactions with ionotropic glutamate and nicotinic acetylcholine receptors, and the degree of protonation is expected to have pharmacological importance in the ion‐channel binding event. Copyright © 2006 John Wiley & Sons, Ltd.

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