1 H NMR STRUCTURAL ANALYSIS OF NOVEL POTASSIUM BLOCKING TOXINS USING A NANO- NMR PROBE MURIEL DELEPIERRE, 1 * ADA PROCHNICKA-CHALUFOUR 1 and LOURIVAL D. POSSANI 2 1 Laboratoire de RMN Institut Pasteur, CNRS URA 1129, 28 rue du Dr Roux, 75724 Paris Cedex 15, France; and 2 Department of Molecular Recognition and Structural Biology, Institute of Biotechnology, National Autonomous University of Mexico, Avenidad Universidad, 2001 Apartado Postal 510-3, Cuernavaca, Mexico 62271 (Received 16 December 1997; accepted 10 April 1998) M. Delepierre, A. Prochnicka-Chalufour and L. D. Possani. 1 H NMR struc- tural analysis of novel potassium blocking toxins using a nano-NMR probe. Toxicon 36, 1599±1608, 1998.ÐA new class of toxin acting on potassium channels and cross-linked by four disul®de bridges instead of three has been recently described. Two peptides, Pi1 and Pi7, puri®ed from the venom of the scorpion Pandinus imperator belong to this new class. Structural features of one of these new toxins, Pi1, have been investigated by proton nuclear magnetic resonance using a new technology that allows to work with very small amount of compound, in the nanomole range. It is shown that it is possible to collect high quality data set in terms of resolution, lineshape and sensitivity with nanomolar amount of compound using this technology. Pre- liminary results on Pi7 are also presented. The approach described here is quite attractive for the study of natural compounds such as toxins often available at low amounts. # 1998 Elsevier Science Ltd. All rights reserved Scorpion venoms are rich sources of different classes of peptides that affect the function of ion channels (Catterall, 1980). They disrupt the normal function of excitable tissues that is muscle and nerves of many animals, including man, by causing respiratory and circulatory damages that can eventually lead to the death. Despite the huge public health problem caused by scorpion stings these peptides represent nice tools for biological research such as neurobiological studies and ion channels characterization. Several toxins have been extensively studied with respect to their structure, mode of action, and localization of the functional site. The most widely known are those specific for sodium and potassium channels (Possani, 1984; Miller, 1995). However, peptides that recognize calcium (Valdivia et al., 1992) and chloride channels (Debin et al., 1993) have also been reported. The sodium channel toxins are, by far, the more important ones in scorpionism while the Toxicon Vol. 36, No. 11, pp. 1599±1608, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0041-0101/98 $19.00 + 0.00 PII: S0041-0101(98)00152-4 * Author to whom correspondence should be addressed. 1599