Characterization of the binding of omega-conopeptides to different classes of non-L-type neuronal calcium channels.
The interaction of two synthetic omega-conopeptides SNX-111 (MVIIA) and SNX-230 (MVIIC) both derived from the marine snail Conus magus, with non-L-type neuronal voltage-sensitive calcium channels (VSCC) in rat brain synaptosomal preparations has been investigated with the aid of well-characterized 125I derivatives of the two peptides. To assess the effects of iodination on the binding characteristics of SNX-111 and SNX-230, the corresponding peptides containing monoiodotyrosine in place of tyrosine, namely, SNX-259 ([127I]SNX-111) and SNX-260 ([127I]SNX-230), respectively, were prepared by solid-phase synthesis. Saturation analysis showed that [125I]SNX-111 and [125I]SNX-230 bound to two distinct classes of high-affinity sites with apparent Kd's of 9 and 11 pM and Bmax's of 0.54 and 2.2 pmol/mg protein, respectively. Kinetic analysis revealed that both peptides exhibited high association rates as well as rapid dissociation rates in contrast to the 125I derivative of the synthetic omega-conopeptide from Conus geographus, GVIA (SNX-124), which binds irreversibly to N-type channels in rat brain synaptosomes. Competition binding experiments with [125I]SNX-111 and [125I]SNX-124 established that both of them bind to the same site, namely, N-type VSCC. The site detected by the binding of [125I]SNX-230 is distinct from N-type VSCC since SNX-111 has very low affinity (K(i) = 135 nM) in competition studies. Recent findings that a novel high-voltage-activated calcium channel in rat cerebellar granule neurons is resistant to blockers of L-, N-, and P-type VSCC but is highly sensitive to SNX-230 suggest that the [125I]SNX-230 binding site may represent this novel type of calcium channel or another, as yet undescribed, VSCC.
Kristipati
R
R
Neurex Corporation, Menlo Park, California 94025.
Nádasdi
L
L
Tarczy-Hornoch
K
K
Lau
K
K
Miljanich
G P
GP
Ramachandran
J
J
Bell
J R
JR
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D002414:Cations, Monovalent / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D008297:Male; D008715:Methionine / Q000031:analogs & derivatives; D008978:Mollusk Venoms / Q000378:metabolism; D007470:Monoiodotyrosine / Q000737:chemistry; D009474:Neurons / Q000378:metabolism*; D010455:Peptides / Q000138:chemical synthesis / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013574:Synaptosomes / Q000378:metabolism; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002414:Cations, Monovalent; D008978:Mollusk Venoms; D010455:Peptides; D020960:omega-Conotoxins; C075851:omega-conotoxin-MVIIC; D016291:Dizocilpine Maleate; C078452:ziconotide; D008715:Methionine; D007470:Monoiodotyrosine; D002118:Calcium