Role of Thr(11) in the binding of omega-conotoxin MVIIC to N-type Ca2+ channels

As replacement of Thr(11) of omega -conotoxin MVIIC with Ala significantly reduced the affinity for both N- and P/Q-type calcium channels, we examined the effect of substitution at this position with other residues. Binding a ssays using rat cerebellar P-2 membranes showed that the affinity is in the order of Leu > Val, aminobutyric acid, Thr > Asn much greater than Ser, Al a, Asp, Phe, Tyr for N-type channels and Thr > Leu, Val, aminobutyric acid, Asn, Ser > Ala much greater than Asp, Phe, Tyr for P/Q-type channels, sugg esting that aliphatic amino acids with longer side chains are favorable for block of N-type channels, The effects of substitution wt re examined elect rophysiologically in BHK cells expressing N-type Ca2+ channels, Inhibition of Ba2+ current by the analogs did not completely correlate with binding af finity, although binding to BHK cells was comparable to rat cerebellar memb ranes. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.