Structure-activity relationships of omega-conotoxins MVIIA, MVIIC and 14 loop splice hybrids at N and P/Q-type calcium channels.
The omega-conotoxins are a set of structurally related, four-loop, six cysteine containing peptides, that have a range of selectivities for different subtypes of the voltage-sensitive calcium channel (VSCC). To investigate the 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 [125I]GVIA radioligand binding assays) and P/Q-type VSCCs (using [125I]MVIIC radioligand binding assays). In these peptides, loops 2 and 4 make the greatest contribution to VSCC subtype selectivity, while the effects of loops 1 and 3 are negligible. Peptides with homogenous combinations of loop 2 and 4 display clear selectivity preferences, while those with heterogeneous combinations of loops 2 and 4 are less discriminatory. 1H NMR spectroscopy revealed that the global folds of MVIIA, MVIIC and the 14 loop hybrid 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.
Nielsen
K J
KJ
Centre for Drug Design and Development, University of Queensland, Brisbane, Queensland, 4072, Australia.
Adams
D
D
Thomas
L
L
Bond
T
T
Alewood
P F
PF
Craik
D J
DJ
Lewis
R J
RJ
D000595:Amino Acid Sequence; D000818:Animals; D002121:Calcium Channel Blockers / Q000737:chemistry* / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D008978:Mollusk Venoms / Q000737:chemistry* / Q000378:metabolism; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D012326:RNA Splicing; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D008978:Mollusk Venoms; D010455:Peptides; D020960:omega-Conotoxins; C075851:omega-conotoxin-MVIIC; C078452:ziconotide