Biochem. J. (2009) 419
(377–385) (Printed in Great Britain)
Identification of a cluster of residues in transmembrane segment 6 of domain III of the cockroach sodium channel essential for the action of pyrethroid insecticides
Yuzhe DU*, Jung-Eun LEE*, Yoshiko NOMURA*, Tianxiang ZHANG*, Boris S. ZHOROV† and Ke DONG*1
*Department of Entomology, Genetics and Neuroscience Programs, Michigan State University, East Lansing, MI 48824, U.S.A., and †Department of Biochemistry and Biomedical Sciences, 4N59 Health Sciences Centre, McMaster University, 1200 Main Street West, Hamilton, Ontario, Canada, L8N 3Z5
A phenylalanine residue (Phe1519) in the sixth transmembrane segment of domain III (IIIS6) of the cockroach BgNav sodium channel is required for the binding and action of pyrethroids. However, whether or not other residues in IIIS6 participate in the action of pyrethroids remains to be determined. In the present study, we conducted a systematic analysis of 20 residues in IIIS6 of the BgNav channel using alanine-scanning mutagenesis. Our results show that alanine substitutions of four residues, Ile1514, Gly1516, Phe1518 and Asn1522, altered sodium channel sensitivity to pyrethroid insecticides. Whereas the G1516A, F1518A and N1522A substitutions diminished sodium channel sensitivity to all seven pyrethroids examined, including four type I (lacking the α-cyano group at the phenoxybenzyl alcohol) and three type II (containing the α-cyano group) pyrethroids, the I1514A substitution enhanced sodium channel sensitivity to four type I and type II pyrethroids that contain the phenoxybenzyl alcohol only. We also show that alanine/lysine substitutions of Leu1521 and Ser1517 affected the action of BTX (batrachotoxin), but not pyrethroids. In the Kv1.2-based homology model of the open sodium channel, side chains of Ile1514, Phe1518 and Asn1522 are exposed towards helix IIS5 and linker IIS4–IIS5, which contain previously identified pyrethroid-interacting residues, whereas Ser1517 and Leu1521 face the inner pore where the BTX receptor is located. Thus the present study provides further evidence for structural models in which pyrethroids bind to the lipid-exposed interface formed by helices IIIS6, IIS5 and linker helix IIS4–IIS5, whereas BTX binds to the pore-exposed side of the IIIS6 helix.
Key words: batrachotoxin, cockroach sodium channel, molecular modelling, pyrethroid insecticide, sixth transmembrane segment of domain III (IIIS6), Xenopus oocyte expression system.
Abbreviations used: BTX, batrachotoxin.
1To whom correspondence should be addressed (email dongk@msu.edu).
Received 14 October 2008/19 January 2009; accepted 20 January 2009
Published as BJ Immediate Publication 20 January 2009, doi:10.1042/BJ20082082
© The Authors Journal compilation © 2009 Biochemical Society
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