Characterization of a novel radiolabeled peptide selective for a subpopulation of voltage-gated potassium channels in mammalian brain.

Judith Racapé,André Ménez,Régine Romi-Lebrun,Sylvaine Gasparini,Martin Kohler,Jessica Liu,Maria L Garcia,Alain Lecoq

doi:10.1074/jbc.m109886200

Abstract

BgK, a 37-amino acid voltage-gated potassium (Kv) 1 channel blocker isolated from the sea anemone Bunodosoma granulifera, can be modified at certain positions to alter its pharmacological profile (Alessandri-Haber, N., Lecoq, A., Gasparini, S., Grangier-Macmath, G., Jacquet, G., Harvey, A. L., de Medeiros, C., Rowan, E. G., Gola, M., Ménez, A., and Crest, M. (1999) J. Biol. Chem. 274, 35653-35661). In the present study, we report the design of two BgK analogs that have been radiolabeled with (125)INa. Whereas BgK(W5Y/Y26F) and its radiolabeled derivative, (125)I-BgK(W5Y/Y26F), bind to Kv1.1, Kv1.2, and Kv1.6 channels with potencies similar to those for the parent peptide, BgK, BgK(W5Y/F6A/Y26F) and its monoiodo-tyrosine derivative, (125)I-BgK(W5Y/F6A/Y26F), display a distinctive and unique pharmacological profile; they bind with high affinity to homomultimeric Kv1.1 and Kv1.6 channels, but not to Kv1.2 channels. Interaction of BgK(W5Y/F6A/Y26F) with potassium channels depends on the nature of a residue in the mouth of the channel, at a position that determines channel sensitivity to external tetraethylammonium. In native brain tissue, (125)I-BgK(W5Y/F6A/Y26F) binds to a population of Kv1 channels that appear to consist of at least two sensitive (Kv1.1 and/or Kv1.6) subunits, in adjacent position. Given its unique pharmacological properties, (125)I-BgK(W5Y/F6A/Y26F) represents a new tool for studying subpopulations of Kv1 channels in native tissues.

Highlights

Voltage-gated potassium (Kv)1 channels regulate numerous cellular processes by controlling plasma membrane potential and electrical excitability [1]
Synthesis of BgK Analogs—To develop new pharmacological tools for studying Kv1 channels, two analogs of BgK, a Kv1 channel blocker isolated from the sea anemone, B. granulifera [22, 23], have been radiolabeled and used to characterize Kv1 channels
Substitution of Phe at Tyr26 and Tyr at Trp5 led to a peptide, (BgK(W5Y/Y26F)), that can be radiolabeled without loss of biological activity

Summary

The abbreviations used are

Voltage-gated potassium (channel); ␣DTX, ␣-dendrotoxin; ChTX, charybdotoxin; DTX-K, dendrotoxin K; HEK, human embryonic kidney; HgTX1, hongotoxin1; 125I-BgK(W5Y/ Y26F), monoiodotyrosine BgK(W5Y/Y26F); 125I-BgK(W5Y/F6A/Y26F), monoiodotyrosine BgK(W5Y/F6A/Y26F); 125I-␣DTX, monoiodo-␣DTX; 125I-HgTX1(A19Y/Y37F), monoiodotyrosine hongotoxin1(A19Y/Y37F). A number of peptides isolated from scorpion, snake, and sea anemone venoms have been characterized and shown to block Kv1 channels by binding to residues located in the external vestibule of the channel [12] Despite their limited selectivity for a given Kv1 subtype, these peptides represent unique pharmacological tools for studying the structure-function relationship of Kv1 channels and have proved to be important for: 1) defining the physiological role that channels play in native tissue, 2) purifying channels from native tissues and determining their subunit composition, and 3) developing the pharmacology of potassium channels [4, 12,13,14,15,16,17,18,19,20]. Given its unique binding properties, 125I-BgK(W5Y/F6A/Y26F) represents a new pharmacological tool for studying subpopulations of Kv1 channels in native tissues

EXPERIMENTAL PROCEDURES

RESULTS

40 Ϯ 3 ND

32 Ϯ 13 647 Ϯ 289

DISCUSSION