Kj. Nielsen et al., Structure-activity relationships of omega-conotoxins MVIIA, MVIIC and 14 loop splice hybrids at N and P/Q-type calcium channels, J MOL BIOL, 289(5), 1999, pp. 1405-1421
The omega-conotoxins are a set of structurally related, four-loop, six cyst
eine containing peptides, that have a range of selectivities for different
subtypes of the voltage-sensitive calcium channel (VSCC). To investigate th
e basis of the selectivity displayed by these peptides, we have studied the
binding affinities of two naturally occurring omega-conotoxins, MVIIA and
MVIIC and a series of 14 MVIIA/MVIIC loop hybrids using radioligand binding
assays for N and P/Q-type Ca2+ channels in rat brain tissue. A selectivity
profile was developed from the ratio of relative potencies at N-type VSCCs
(using [I-125]GVIA radioligand binding assays) and P/Q-type VSCCs (using [
I-125]MVIIC radioligand binding assays). in these peptides, loops 2 and 4 m
ake the greatest contribution to VSCC subtype selectivity, while the effect
s of loops 1 and 3 are negligible. Peptides with homogenous combinations of
loop 2 and 4 display clear selectivity preferences, while those with heter
ogeneous combinations of loops 2 and 4 are less discriminatory. H-1 NMR spe
ctroscopy revealed that the global folds of MVIIA, MVIIC and the 14 loop hy
brid peptides were similar; however, several differences in local structure
were identified. Based on the binding data and the 3D structures of MVIIA,
GVIA and MVIIC, we have developed a preliminary pharmacophore based on the
omega-conotoxin residues most Likely to interact with the N-type VSCC. (C)
1999 Academic Press.