AA sequence: Phe-Asn-Trp-Arg-Cys5-Cys6-Leu-Ile-Pro-Ala-Cys11-Arg-Arg-Asn-His-Lys-Lys-Phe-Cys19-NH2
Disulfide bonds: Cys5-Cys11 and Cys6-Cys19
Length (aa): 19
Formula: C105H160N36O21S4
Molecular Weight: 2390.90 Da
Appearance: White lyophilized solid
Solubility: aqueous buffer
CAS number: not available
Source: Synthetic
Purity rate: > 95 %
Rho-Conotoxin-TIA
135 $ – 550 $
Blocker of α1-adrenoreceptor
Rho-conotoxin TIA is a conopeptide that has been isolated from the venom of the fish-hunting marine cone snail Conus tulipa. Rho-conotoxin TIA is a selective antagonist of α1-adrenoreceptor (α1A-, α1B– and α1D-AR). It acts non-competitively onto α1B-adrenoreceptor but competitively on α1A-adrenoreceptor and α1D-adrenoreceptor. The most important residue for activity is Arg4. Rho-conotoxin TIA is 10-fold selective for human α1B-adrenoreceptor over α1A-adrenoreceptor and α1D-adrenoreceptor. The IC50 values for Rho-conotoxin TIA for inhibition of 125I-BE were 18 nM for human α1A-AR, 2 nM for α1B-AR and 25 nM for α1D-AR.
Allosteric alpha1-Adrenoreceptor Antagonism by the Conopeptide rho-TIA
A peptide contained in the venom of the predatory marine snail Conus tulipa, rho-TIA, has previously been shown to possess alpha1-adrenoreceptor antagonist activity. Here, we further characterize its pharmacological activity as well as its structure-activity relationships. In the isolated rat vas deferens, rho-TIA inhibited alpha1-adrenoreceptor-mediated increases in cytosolic Ca2+ concentration that were triggered by norepinephrine, but did not affect presynaptic alpha2-adrenoreceptor-mediated responses. In radioligand binding assays using [125I]HEAT, rho-TIA displayed slightly greater potency at the alpha 1B than at the alpha 1A or alpha 1D subtypes. Moreover, although it did not affect the rate of association for [3H]prazosin binding to the alpha 1B-adrenoreceptor, the dissociation rate was increased, indicating non-competitive antagonism by rho-TIA. N-terminally truncated analogs of rho-TIA were less active than the full-length peptide, with a large decline in activity observed upon removal of the fourth residue of rho-TIA (Arg4). An alanine walk of rho-TIA confirmed the importance of Arg4 for activity and revealed a number of other residues clustered around Arg4 that contribute to the potency of rho-TIA. The unique allosteric antagonism of rho-TIA resulting from its interaction with receptor residues that constitute a binding site that is distinct from that of the classical competitive alpha1-adrenoreceptor antagonists may allow the development of inhibitors that are highly subtype selective.
Sharpe I., et al. (2003) Allosteric alpha1-Adrenoreceptor Antagonism by the Conopeptide rho-TIA. JBC. PMID: 12824165
Subtype-selective noncompetitive or competitive inhibition of human α1-Adrenergic receptors by rho-TIA
The 19-amino acid conopeptide (rho-TIA) was shown previously to antagonize noncompetitively alpha(1B)-adrenergic receptors (ARs). Because this is the first peptide ligand for these receptors, we compared its interactions with the three recombinant human alpha(1)-AR subtypes (alpha(1A), alpha(1B), and alpha(1D)). Radioligand binding assays showed that rho-TIA was 10-fold selective for human alpha(1B)-over alpha(1A)- and alpha(1D)-ARs. As observed with hamster alpha(1B)-ARs, rho-TIA decreased the number of binding sites (B(max)) for human alpha(1B)-ARs without changing affinity (K(D)), and this inhibition was unaffected by the length of incubation but was reversed by washing. However, rho-TIA had opposite effects at human alpha(1A)-ARs and alpha(1D)-ARs, decreasing K(D) without changing B(max), suggesting it acts competitively at these subtypes. rho-TIA reduced maximal NE-stimulated [(3)H]inositol phosphate formation in HEK293 cells expressing human alpha(1B)-ARs but competitively inhibited responses in cells expressing alpha(1A)- or alpha(1D)-ARs. Truncation mutants showed that the amino-terminal domains of alpha(1B)- or alpha(1D)-ARs are not involved in interaction with rho-TIA. Alanine-scanning mutagenesis of rho-TIA showed F18A had an increased selectivity for alpha(1B)-ARs, and F18N also increased subtype selectivity. I8A had a slightly reduced potency at alpha(1B)-ARs and was found to be a competitive, rather than noncompetitive, inhibitor in both radioligand and functional assays. Thus rho-TIA noncompetitively inhibits alpha(1B)-ARs but competitively inhibits the other two subtypes, and this selectivity can be increased by mutation. These differential interactions do not involve the receptor amino termini and are not because of the charged nature of the peptide, and isoleucine 8 is critical for its noncompetitive inhibition at alpha(1B)-ARs.
Chen Z., et al. (2004) Subtype-selective noncompetitive or competitive inhibition of human α1-Adrenergic receptors by rho-TIA. JBC. PMID: 15194691
Differential Distribution of Functionalalpha1-Adrenergic Receptor Subtypes along the Rat Tail Artery
The rat tail artery has been used for the study of vasoconstriction mediated by alpha(1A)-adrenoceptors (ARs). However, rings from proximal segments of the tail artery (within the initial 4 cm, PRTA) were at least 3-fold more sensitive to methoxamine and phenylephrine (n = 6-12; p < 0.05) than rings from distal parts (between the sixth and 10th cm, DRTA). Interestingly, the imidazolines N-[5-(4,5-dihydro-1H-imidazol-2-yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl]methanesulfonamide hydrobromide (A-61603) and oxymetazoline, which activate selectively alpha(1A)-ARs, were equipotent in PRTA and DRTA (n = 4-12), whereas buspirone, which activates selectively alpha(1D)-AR, was approximately 70-fold more potent in PRTA than in DRTA (n = 8; p < 0.05). The selective alpha(1D)-AR antagonist 8-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione dihydrochloride (BMY-7378) was approximately 70-fold more potent against the contractions induced by phenylephrine in PRTA (pK(B) of approximately 8.45; n = 6) than in DRTA (pK(B) of approximately 6.58; n = 6), although the antagonism was complex in PRTA. 5-Methylurapidil, a selective alpha(1A)-antagonist, was equipotent in PRTA and DRTA (pK(B) of approximately 8.4), but the Schild slope in DRTA was 0.73 +/- 0.05 (n = 5). The noncompetitive alpha(1B)-antagonist conotoxin rho-TIA reduced the maximal contraction induced by phenylephrine in DRTA, but not in PRTA. These results indicate a predominant role for alpha(1A)-ARs in the contractions of both PRTA and DRTA but with significant coparticipations of alpha(1D)-ARs in PRTA and alpha(1B)-ARs in DRTA. Semiquantitative reverse transcription-polymerase chain reaction revealed that mRNA encoding alpha(1A)- and alpha(1B)-ARs are similarly distributed in PRTA and DRTA, whereas mRNA for alpha(1D)-ARs is twice more abundant in PRTA. Therefore, alpha(1)-ARs subtypes are differentially distributed along the tail artery. It is important to consider the segment from which the tissue preparation is taken to avoid misinterpretations on receptor mechanisms and drug selectivities.
Kamikihara SY., et al. (2005) Differential Distribution of Functionalalpha1-Adrenergic Receptor Subtypes along the Rat Tail Artery. JPET. PMID: 15872040